MadSci Network: General Biology

Re: How do insects drink?

Date: Mon Dec 13 05:42:40 1999
Posted By: Justin Roux, Engineering and Physiological Scientist.
Area of science: General Biology
ID: 942956090.Gb


What a great question. It's nice to hear from people who think deeply 
about our six-legged friends. As a simple answer, yes, insects do drink in 
the same way as other animals, but there is a little more to it than that.

Firstly, it depends on the rest of the insect's diet as you rightly point 
out. Many herbivorous insects get the majority, if not all, of their fluid 
from the food they eat because vegetation has such a high water content. I 
have some tropical stick insects and they certainly get all their water 
from the leaves they eat, although they are kept in a damp environment. It 
is also worth noting that their mouthparts are not particularly effective 
for drawing water anyway.

It is not uncommon for insects to drink from the morning dew, from 
raindrops, or from the surfaces or edges of ponds. Leave a damp tissue out 
on a hot day (make it bright yellow to attract the most insects) and watch 
them come in to drink. If you watch with a magnifying glass you will see 
that they have many different ways of doing it; flies suck it up, and 
wasps use a tiny structure that looks much like a tongue. While mentioning 
wasps, it is worth thinking about nest building which is done by biting 
tiny pieces of wood and bark and chewing them into a paste from which the 
nest is made. This requires water and so the wasp needs to take on 
moisture for this purpose too. I have two giant millipedes (not insects, 
but arthropods all the same) that augment their cucumber and tomato diet 
with a considerable amount of water that they draw from the damp soil 
around them.

As a general rule, the ability to go without water is confined to small 
animals, and the larger an animal is, the more it depends on water. This 
could suggest why the bigger insects are usually to be found in warm wet 
places such as the rainforests. 

Finally, to answer your question about carnivorous insects, lets look at 
robber flies and mantids. Both are ambush style predators, one of which is 
common worldwide, whereas the other is usually only found in warmer 
climates. Both have a diet that is made up of prey, but the robber fly 
will take juice from fruit and the mantis will sip water from leaves when 
it gets thirsty.

The next time you're drinking lemon soda on a hot day, spill a little and 
watch what the wasps do. Obey your thirst - or whatever the advert says.


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