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Each and every which way


 
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Dr Ken Walker, Senior Curator for Insects at Museum Victoria, looks at some of the ingenious behaviours of insects, some going to extraordinary lengths to protect their larvae. While there are 8,000 species of birds in the world and 300,000 different species of flowering plants there are more than 500,000 different species of beetles and an estimated insect population of between 10 and 30 million worldwide. Many insects have adapted to their environments in ways which suggest they have intelligently used those habitats.

 
Ocelli (Ken Walker)
Nearly all insects have two eyes on the sides of their head and they also have three false eyes, known as ocelli. The ocelli tell each insect what time of the season it is so butterflies, for instance, know when to stop laying eggs as autumn approaches. What is extraordinary is that the ocelli avoid unseasonal variations in temperature and measure the day length so each season can be distinguished. Shorter and shorter days are leading into winter; longer and longer ones are leading into summer.

 
Insects cannot detect red light so colonies of ants for example can be viewed through red covered lights, tricking the ants into thinking it is night. Insects have in fact shifted their vision colour spectrum. They can’t see red, which is at the low end of the spectrum but they can see ultraviolet light which is at the high end. For bees, this means that they can detect the best ways to get to pollen in flowers, a positive benefit of such a spectrum shift.

 
Atta  or Palisade ants (Adrian Pingstone)

 
Another unusual insect behaviour is that of a particular ant that gathers a food to make another food, an activity akin to farming. The palisade ant (or Atta ant) gathers a green leaf which is transported back to the colony where it is macerated into a green pulp. Then the pulp is inoculated with a fungus which comes from injecting ant saliva into the pulp. The fungi continue to grow, their spores providing food for the ant larvae.
The human botfly which occurs in South America has an amazing way of getting its eggs onto hosts such as humans and other warm-blooded creatures. The botfly will catch a blood sucking insect like a mosquito on the wing . It doesn’t kill it, but lays its eggs on the outside of the mosquito’s body and lets it go.

 
Botfly maggot (http://www.surroundscience.worpress.com)
When the mosquito bites a warm blooded creature, the body heat from the mosquito’s victim causes the eggs to hatch and the larvae burrow into the skin of the unsuspecting host. The maggots cause boil-like wounds and any people who have returned from holidays in South America with such boils have gone to doctors to have their boils lanced only to find a maggot inside each one.

 
The spider hunting wasp also uses hosts to feed its larvae.. It will catch a spider, usually something like a huntsman, stinging it but not killing it. It then drags its victim spider to a hole in the ground, lays an egg on the spider and covers the hole. The egg will hatch and it immediately burrows into the still-paralysed spider.

 
Spider hunting wasp (Johnragla)
The wasp larva knows which bits of the host to eat first so the spider stays alive for as long as possible. It eats the fatty tissue first and while it attacks things like muscles it does not yet attack the heart or the brain. The spider is literally eaten inside out before the larva eventually kills it.
Another wasp attacks orb-weaving spiders. The wasp lays an egg on the spider in its web. Just like the spider hunting wasp, the larva feeds on the still alive spider.

 
Wasp eggs on Orb weaving spiders (Ken Walker)
However, in an amazing development, it injects its host with a chemical which forces the spider to spin a cocoon around itself, in effect spinning the spider’s own death shroud to the benefit of the young wasp.
In the insect world it seems that repellent insects came before insect repellent.

Dr Ken Walker was interviewed for A Question of Balance by Ruby Vincent. Images provided by Dr Walker. Summary text by Victor Barry February 2014 and re edited November 2016.

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