Monday, December 18, 2006

Leaping larvae

Snail mentioned "cheese-skippers", the jumping maggots of the carrion flies (Piophilidae).

It's slightly less obvious why piophilids are called cheese-skippers. You need to see the maggots at work before the common name makes sense. When disturbed, they curl up, grabbing their ... ahem ...anal papillae with their mouthparts. And then they let go, springing several centimetres into the air. Boo!

Jumping in dipteran larvae additionally occurs in several other, taxonomically diverse families. These include Tephritidae (fruit-flies), Cecidomyiidae (gall midges), Agromyzidae (leaf miner flies), Clusiidae (umm...?) and Phoridae (scuttle flies). (Phew, those are a few fly families that you don't come across very often! I wouldn't know a cecidomyiid from Adam!).

Additionally, jumping has been noticed in the Neriidae (long-legged flies). The neriid that occurs in Sydney is Telostylinus angusticollis. This animal is cultured at UNSW and used for studies of sexual selection and aging, as the males have exaggerated features and fight for resources and access to females.

That's a female pictured on the left; males are more slender and elongate. They fight head-to-head, striking each-other with their front legs, heads and antennae. Males also put those long legs to use standing guard over a female - literally.

Larvae of the species, pictured top and bottom, develop in rotting bark, such as that of Acacia longifolia. When they are close to pupation, they evacuate the gut, emerge from their substrate, and at this stage are thought to use jumping as a way of getting off their tree and getting to the soil where they are thought to pupate.

This photo shows what a larva looks like before (left) and after (right) evacuating its gut. Only when it's done this does it gain the ability to jump.

You can see the mechanism in the top photo - the maggot reaches around, grabs a 'ledge' between its last two abdominal segments using its oral hooks, then it contracts its longitudinal muscles. This builds up tension which is then released when the oral hooks are disengaged. Pop!

They're not terribly good jumpers. Not like piophilids which can jump about 50 cm from the surface of a corpse. No, these guys have a lot of trouble jumping from a horizontal surface. They actually do it best if they're upside down - they'll hang off, suspended by their rear ends, before reaching up and jumping downwards off the surface. But put one on a dry surface and crawling doesn't work, so it will wriggle around and try to jump. Normally it doesn't work so well (as in the top photo), as the larva will be lying on its side and therefore not have a great deal to push off.

Jumping in fly larvae is a novel solution to the problem of moving fast and far if you're a small soft-bodied organism. The place where the larva grows up, be it rotting bark, a piece of fruit or a decaying corpse, is generally not a great place to pupate. And a juicy maggot in the open is vulnerable to predation, parasitism, dessication... With a couple of quick jumps, a larva can get away from its food source without crawling laboriously over its surface, settle down and start the business of metamorphosis.

5 comments:

Snail said...

Excellent post, David. (Oh well, they're all excellent. You know what I mean.)

Deidre actually made a video of the piophilids from the carrion experiment. It kept us amused for quite some time. (It was much less of an olfactory assault than watching them in situ.)

Perhaps the Clusiidae are the Not-now-Cato flies?

Darky said...

Why, snail?
Because they make excruciating jerks?

Snail said...

Clouseau.

"Not now, Cato" from A Shot in the Dark.

(Not one of my better attempts at humour!)

Darky said...

(Not one of my better attempts at humour!)

And not one of mine either, apparently ;-/

I love A Shot in the Dark and am now about to translate my attempt at an Inspector C accent.

because they make excruciating j o k e s

Well, that was a real fizzer, ay. :-)

Darky said...

They could probably even make jerks on the fern.