E-I-E-I-O

It is an undeniable fact that as a species we are the dominant animal on the planet. We compliment ourselves on the fact that this dominance is due to our intelligence and ingenuity, the occurrence of which is thought to have arisen from the increased nutrition and resource availability and release from foraging time brought about by the agricultural revolution. The revolution has fuelled the quest for knowledge that makes our species unique; particularly knowledge of other life - be it terrestrial or beyond. Most people would agree that there are other animals on the planet that show forms of intelligence close to our own, but in my experience perceptions tend to be restricted to analogous mammalian groups. It is interesting, then, to discover that this agricultural behaviour has actually evolved nine other times in the animal kingdom, in each case among the insects. Having begun so grandiose in my introduction, it is to the ants, termites and ambrosia beetles we now look.

Atta cephalotes at work on their fungus farm

With 220 species of ants from the tribe Attini ('Attine' ants), 3400 species of ambrosia beetles (a subfamily of weevil, Scolytinae) and 330 termite species from the Macrotermitinae subfamily, our species gets few innovation points for our farming behaviour. However as with all convergent evolution, the same behaviour is achieved in slightly different ways. Where we are above-ground plant growers, all these species are growers of fungus away from light, and where we maintain other culinary prospects, these all these species rely on their cultivated fungi for their only source of sustenance. 

Ant fungiculturalists (for which you can also visit this blog) use a variety of fresh organic substrates on which to grow fungi, from leaves and flowers to seeds and wood. The specific fungus used by each colony is passed on to daughter queen ants before they leave the nest. They transport a sample of the cultivar in pouches present in their mouth-parts and use it to establish their own gardens. Similarly, termite fungiculturalists are specialised to a single genus of fungi, that of Termitomyces, and their life cycle is synchronised with the fruiting of the fungus. Special chambers are allocated inside termite mounds for fungal growth, and they grow their gardens on dead or partially decomposing plant material. Ambrosia beetles tunnel into the wood of trees and maintain the fungal growth that occurs on the excavated walls. Like the ants, these beetles also transport their fungus from old to colonising areas, but instead of mouth pouches, the beetle uses specialised pouches along their body. However, unlike the Attini and termites, an ambrosia beetle's fungal garden is cared for only by the colonising female, which means that if she dies, the fungi will overrun her brood. All three types of insect gardens are also a diverse culture of bacteria and yeasts.

Ambrosia beetle larvae in fungus-lined tunnels

For 50 million years of agricultural success to our 10 thousand years, you might expect these farmers to be experts on agricultural sustainability. So, to maintain our intelligence, we must ask: what can we learn from these insects?

The fungus Termitomyces on a termite mound

Plant mono-cultures are often identified as one of the weaker aspects of our own husbandry of the land, as minimal diversity opens systems to more effective removal by a single pathogen. Yet all farming insects use mono-cultures. They minimise the problems of such systems using a combination of strategies: isolating and sealing gardens underground to reduce potential for infection, continuously monitoring crops using a myriad of workers, maintaining genetic diversity of the crops by trading cultivars amongst populations, and managing microbes that suppress crop diseases. 

Of these techniques, microbial management of plants seems the most practical and likely option for improving our own agricultural systems. Microbes are known to increase pathogen resistance in some of our own crops, but the microbial composition of the soil is difficult to control. Prior to planting, insects farmers will partially or completely sterilise the substrate into which they plant their fungi. Designing our own agricultural systems to more effectively take advantage of beneficial microbes is a step in the same direction as these green tarsal-clawed gardeners.

It seems that, while our search for intelligent life continues, intelligent lifestyles are right under our toes. 

I cannot recommend The Evolution of Agriculture in Insects by Mueller, Gerardo, Aanen, Six and Schultz enough. And thanks to xkcd for the cartoon catalyst.

A Garfield Favourite

Insects Are Cool, Too

One of our esteemed Entomology lecturers has for the past few weeks been preaching doom and gloom about the immediate future of ENTO304 participants’ insect collecting prospects. ‘Hope you've done all your collecting: it’s getting too cold for insects!’ he warns us. ‘The weather’s turning!’ And it’s true. If there’s one thing that’s good about winter, it’s the diminishing of pesky houseflies in our flat. It came as some surprise, then, when I discovered a whole book dedicated to the Entomology of Antarctica. When I think of life in Antarctica, I think penguins, and that’s pretty much as far as I get. But what if I were to tell you that the biggest terrestrial animal in Antarctica is actually an insect? What if I were to add that there are more insect species in Antarctica than any other Antarctic animal?

How can this be? What does Antarctica have to offer insects apart from ice? Not much, it turns out, but enough…

I use ‘insect’ in the loosest term: from sea-level to 2000 metres above, Antarctica is home to over 50 species of arthropod. They can be divided into two categories based on the type of habitat they exploit: half are the the-answer-is-right-under-your-nose parasitic kind, and half are the how-on-earth-do-they-do-it free-living kind.

Antarctica: more than just penguins

The parasitic arthropods, which include lice, ticks, a single species of flea and parasitic mites, are probably the easiest to understand. Sucking lice live on the seals of Antarctica, and ticks, biting lice and parasitic mites live on Antarctica’s birds. Even when diving, warm-blooded animals are able to provide these invertebrates with a much warmer habitat than could otherwise be found, and a considerably greater stability of microclimate which means such arthropods need little in the way of their own homeostatic mechanisms. Parasitism is also the obvious choice in a depauperate environment in terms of a ready and guaranteed food supply. Desiccation, the main adversary of the free-living insects, is significantly less of a problem for creatures small enough to live under the protective, waterproof layers of feathers or fur. Colony behaviour of the majority of Antarctic birds and seals facilitates the dispersal of these invertebrates.

Not all of Antarctica is covered in ice, and not all of it is covered in ice all year round. Antarctica’s free-living arthropods - midges, springtails and non-parasitic mites – can be found in habitats involving such diverse geomorphology as snow-melt streams, old lava flows, freshwater or brackish ponds, scree-slopes, moraine deposits, soil and exposed stone. Because all Antarctica’s large vertebrate fauna are marine rather than terrestrial, these arthropods are Antarctica’s only terrestrial animals. 

Antarctica: more than just penguins with lice

Compared to the parasites, the free-living arthropods are much more subject to the forbidding environment that we normally associate with Antarctica: extreme cold and extreme dryness. Temperature, as with all insects, determines activity levels of these arthropods and thus habitats that receive the most sun in summer, such as northward facing slopes, are more frequently inhabited. Though generally preferring of the dark, the warmed rocks provide a microclimate that allows the arthropods to move. Ultimately, however, arthropod distribution is restricted by moisture. 

Antarctic mites

The free-living arthropods live in close proximity to plants, which in Antarctica means mosses, lichens and algae; though fungi, liverworts and grasses may be found in more northern areas. These primary producers provide the invertebrates with food and moisture. Combined, this is the simple entirety of Antarctica’s terrestrial ecosystem. Springtails, the least desiccation-tolerant, are usually found amongst moss roots, while mites, the hardiest, inhabit a wider variety of rocky areas which can be comparatively drier - porous rock cavities and the underside of shales near temporary melt-water rivulets are common habitats.

Two Belgica antarctica

You can’t get very far into Antarctic entomology without coming across Belgica antarctica: Antarctica’s largest (roughly 0.5 cm long) endemic terrestrial species and the flightless version of only two true Antarctic insects, the midge. This species breeds in brackish waters and lives near pools and streams associated with mosses. Recent studies on B. antarctica have found that, due to their high desiccation tolerance, the midge larvae are able to utilise a vapour gradient in the presence of ice that reduces the melting point of their body fluids so they don’t freeze over winter. All the free-living arthropods are dormant through the winter in whatever developmental stage they have reached. Few populations of any of these arthropods show great annual stability, changing seasonally according to local migrations in response to moisture gradients. Suitable areas of habitation are also those that are sheltered from Antarctica’s strong winds, which can increase the rate of desiccation and lower temperatures; though it may be a dispersal mechanism for springtails which have been collected from the air with nets.

Perhaps it is ironic or perhaps it is poetic that the largest land mass in the southern hemisphere should have the smallest terrestrial ecosystem consisting of some of the smallest macroscopic life, or perhaps it is just amazing that such animals can be found here at all. Regardless of your take, the fact remains: Antarctica is more than just penguins. 

Antarctic springtails amongst moss

Thanks to Insect Habitats in Antarctica by J. L. Gressitt and R. E. Leech for opening my eyes.

Long Legs and a Long Way to Grow

Just to continue with the long-legged theme of my blug so far, here's a quick share of something that made me smile when I walked into our bathroom the other week:

This type of spider is what I have always known as a daddy long-legs (or in this case, a baby long- legs) from the family Pholcidae. They can grow to be very big and usually hang upside-down in untidy, irregular webs of their own creation... but this tiny novice seemed perfectly content hanging from a ready-made hair on the side of our (otherwise quite immaculate) basin.

The Crane Fly Calamity

It’s a tale of childhood woe: a school yard during lunch time. Rain drums meditatively on the classroom roof and sheets off the verandah gutters into the mists of recollection. Children, as game as they ever were, race the length of the classroom verandahs with cricket bats, their squeals and shouts energising the greyness of the average autumn day. From out of the deluge a lone creature flies falteringly, gangly legs dangling as it drunkenly intercepts the verandah wall. Having found a dry oasis, it lodges spread-eagled under the white roof above where a dozen others of its kind also shelter from the storm. But no less muffled by memory than the massacre that follows is the war cry of the children as they hoist their cricket bats: ‘Kill the mosquitoes!’ The Crane Fly has escaped a watery grave only to meet its fate in the swing of ignorance.

Crane flies are not mosquitoes. ‘Crane fly’ is one of many common names that typically encompasses the families Tipulidae (true crane flies), Limoniidae (Limoniid crane flies), Cylindrotomidae (long-bodied crane flies) and also sometimes Pediciidae (hairy-eyed crane flies), all of which can be included in the superfamily Tipuloidea. Elsewhere in the world, crane flies are known as daddy long legs, gollywhoppers and even mosquito eaters (yet another myth of the  misunderstood Tipulidae, who literally wouldn't hurt a fly). Larvae are often used by fishermen for trout bait, and these immature forms of Tipulidae are colloquially known as leatherjackets. Mosquitoes, on the other hand, fall into the single family of Culicidae. Apart from the larval name of ‘wriggler’, the only variation to their common name is probably just the choice of expletive used to refer to them after being bitten. 

Types of flies referred to as ‘crane flies’, roughly in order from left to right of family relatedness to true crane flies.

Both crane flies and mosquitoes are of the Diptera order (as both have only two wings and a pair of halteres), but they are only related to the extent of the suborder Nematocera. The oldest Tipuloidea fossils date back to around 240 million years (lower Triassic period), while most Culicidae fossils are around 38 thousand years old - though it is thought Culicidae diverged some time during the Jurassic period. Although the relationships within crane flies, like so much else in taxonomy, are under constant review (for the latest, see here), as are the phylogenetic relationships within Nematocera (if you’re so inclined, there’s some bed time reading in this too), the distinctness of crane flies to mosquitoes is not uncertain due to a variety of morphological and biological differences.

A widely accepted phylogeny for the lower Diptera (Nematocera), showing the superfamiliy Culicomorpha (containing Culicidae species) in relation to the superfamily Tipuloidea (containing Tipulidae species).

Both mosquitoes and crane flies are semi-aquatic holometabolous insects, as they have a larval and pupal stage in their life cycle which relies on water. For mosquito species, larvae are found in all kinds of standing water bodies, such as streams, ditches, ponds and puddles, and some species have a relatively high salinity tolerance. Tipulid larvae require moisture so they don’t dry out, but inhabit wet terrestrial habitats such as soil or rotting plants, and are restricted to fresh water. As with many Dipterans, it is when mosquitoes and crane flies are in their larval stage that they show the most perceptibly distinct morphology.

Mosquito larva  floating just under 

the surface of the water facing 

downwards (left) and a bird's-eye 

view of a fat crane fly larva (right), 

head at the top.

Unlike crane flies, mosquito larvae have eyes on either side of an ovoid head, and a ‘moustache’ of bristles above the mouthparts, as well as numerous hair-like projections all over the body. Most species filter microorganisms and organic matter, though some eat the larvae of other mosquito species. The breathing tube near the end of their abdomen is probably the most characteristic structure of Culicidae larvae - it means they float at the surface of the water. Crane fly larvae have breathing siphons at the end of their abdomen and tend to feed on decomposing plant leaves and associated microflora, or munch on the roots of living plants. All life stages of both these insects are important food sources for fish, birds, amphibians and other insects higher in the food chains of the environments they inhabit. 

Different sizes: crane flies can be BIG. 

Mosquitoes will never want to present 

that much of a target.

Granted, adult mosquitoes and crane flies have a superficial resemblance in that they both have long legs. However, compared to body size, crane flies’ legs are much longer than mosquitoes’ legs (compare the second photo of the Culicid to that of the Tipulid at the end of this post). The average crane fly is also quite big, though often Limoniid crane flies will be a similar size to mosquitoes. Some mosquito legs are striped white, so as to seem ethereal. When threatened, mosquitoes will hold one or both of their hind legs above their body in a characteristically curved position (consult the shadow of the first Culicid picture at the end of this post – you might need to duck down slightly to see them on your screen). True crane flies show and do neither of these things. Also, the structure of mosquitoes’ feet allow them to cling to smooth vertical surfaces, while true crane flies have a great deal of trouble with this. They can often be seen bobbing around windows or sliding and scraping along smooth surfaces searching for footholds, while mosquitoes try their hardest not to be seen.

Crane fly flight can be recognised as the kind that will never win any races (i.e. slow, cumbersome and generally erratic) due to their long legs; some crane flies have recognised a lost cause when they are one and taken up flightlessness instead (yes, Chionea species, I’m looking at you). When at rest, true crane flies hold their wings away from their body, while mosquitoes fold their wings. Mosquito wings have thick setae (bristles) along both sides of the wing veins (which make the wings look quite furry under the microscope) and are highly scleritised (hardened) at the base of the wing, unlike Tipulidae. Like all winged insects, crane flies and mosquitoes have unique wing venation that makes them distinct. For example, the subcoastal vein (Sc) ends at the coastal vein (C) in mosquitoes but in crane flies ends at the first radial vein (R₁). Mosquitoes also have just one anal vein (A) while crane flies have two, and crane flies also have a discal cell (dm) that is absent in mosquitoes. 

Wings of Culiseta species versus wings of Tipula species

Though burdened fliers, all crane flies do so uncomplainingly and silently; this is not the case for mosquitoes where some species, such as the tiger mosquito (Ades albopictus), make that dreaded high-pitched whining sound we all know and hate. Male mosquitoes use this sound to locate females; crane flies travel blindly to encounter mates if there are none immediately present after emergence from the pupal stage.

Head morphology - including 
mouth-parts - of a crane fly 
(top) and  penetration of 
the stylets of a mosquito 
(bottom).

If you’re still not convinced that crane flies aren't just overgrown mosquitoes in a good disguise, let the mouth-parts be the clincher for you. There would be no war on mosquitoes if it weren't for the bloodsucking, disease-spreading ways of the majority of females, as permitted by her specialised mouth-parts: a permanently extended, rigid stylet for piercing and sucking (due to elongation of the maxillae and labrum, which remain comparatively short, separate appendages in crane flies), sheathed by a similarly elongated flexible lower lip, or ‘labium’ (also significantly shorter in crane flies). Like male mosquitoes, crane flies of both sexes feed on nectar or not at all, and have a life span of only a few days or weeks. Prolonged rain can mean that crane flies starve to death. 

Further morphological differentiations include that of the antennae, which vary in crane flies but are most commonly moderately short, thin and of thread-like or bead-like form. Mosquitoes have plumose (feathery) antennae. The presence of the ‘transverse V’ or ‘V-shaped mesonotal suture’ - a groove on the thorax between the bases of the wings - is also an identifier of Tipulidae in taxonomic keys.

Both mosquitoes and crane flies have a world wide distribution and there is much diversity across species within both of these families. New Zealand has 15 species of mosquito, with high endemism: only 3 species are found elsewhere. If you want to familiarise yourself on each of the New Zealand mosquitoes, visit New Zealand BioSecure. Crane flies also show high species endemism at a global scale. New Zealand has comparatively more species of crane fly than mosquito (around 600 species) and the most common of these are usually native species from the genus Leptotarsus, often present in gardens. If you want to know more about these or any species of crane fly from any country, you can search at Crane Flies of the World. 

So spread the word! Let crane fly knowledge infiltrate the population in a way similar to but distinctly unlike the spread of malaria in Africa...

...Crane flies are not Mosquitoes. 

A crane fly versus two vantages of a 5-legged mosquito.

I couldn't have written this without:

•  Biology of Tipulidae by G. Pritchard (1987)
• The Anatomical Life of the Mosquito by R. E. Snodgrass (1959)
• Global Diversity of Mosquitoes (Insecta: Diptera: Culicidae) in Freshwater by L. M. Rueda (2007)

Pictures of the different types of crane flies (Tipulidae, Cylindrotomidae, Pediciidae, Limoniidae, Trichoceridae, Tanyderidae and Ptychopteridae) were compiled by me. The phylogeny, Tipula wing venation, Tipula wing image, and Culiseta wing image have all been modified.