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> > We have started to hear crickets sing in the last week or two. In so Hi Angus, On part (1) below, you gave up too easily and obviously need to think more like a caterpillar. I used to rear a few species (mostly moths) as a kid in the UK and encountered the following defensive reactions, at least when I went near caterpillars or tried to touch them (might vary if the approach was from a wasp, and obviously wasps aren't the only things that eat caterpillars, either). - drop like a stone off a leaf or stem on to the undergrowth or soil below, making itself difficult to find; climb back up later (some noctuids would do this). - curl up into a millipede-like tight circle with defensive bristles sticking out, that may be noxious to some predators, or make parasitoids harder to gain a close approach to oviposit. Some tiger moths (arctiids) do this. Somebody is going to ask why the nasty irritating hairs break off so easily and I don't know, but presumably there's a weak spot near the base that's responsible. 'Deliberately' weakened areas underlie defensive reactions called 'autotomy' elsewhere, as when a crab defensively sheds a leg at the leg's specialized autotomy zone. - regurgitate noxious fluid from the mouthparts, that may smell bad and deter some attackers, suggesting a potentially unpleasant meal if pursued. This would be more common in insects like grasshoppers. - defensive writhing of the back end with the prolegs still attached to a stem, presumably in an attempt to prevent the predator or parasitoid gaining a foothold. I've seen a sphinx caterpillar here do this. - defensive front-end rearing to show fearsomely threatening eyespots - large elephant hawk moth caterpillars in UK do this (Deiliphilia elpenor, spelling from memory). - defensive rearing or writhing to remind predator of warning coloration that advertizes toxicity: orange-black banded cinnabar moth caterpillars (an arctiid? - I can't remember) that live in small colonies on ragwort do this. I was once involved in breeding these en masse for pocket money, in an ill- conceived scheme to export pupae to Australia to control invasive ragwort, bad for livestock. Apparently someone forgot that the seasons are 6 months out of sync so the adult moths emerged in winter. No doubt the lep specialists here or others can add a few more tricks? Re. damned if you do or don't, biologists view these sorts of adaptations as evolutionary 'arms races'. The prey species evolves a new or modified defense, then the predator evolves a countermeasure; well known in plants too. Usually, neither strategy is perfect so an equilibrium prevails for a while: sometimes a defense succeeds and sometimes it fails. On (2), as you may know, one of the largest groups of brachyceran flies, tachinids, reproduce almost exclusively by parasitizing other insects either in the adult or larval state. They lay one or more eggs on the body of the insect host and the fly larvae slowly eat it up from the inside and then pupate, a pretty gruesome fate. A question is, how do they locate the host? There are a couple of genera of tachinids, one of which is a yellowish nondescript fly Ormia, that home in on singing male crickets, as you say. According to work done in Ron Hoy's lab in Cornell Univ, the fly shows quite exceptional directional selectivity of around 1°, so can accurately/quickly locate the sound source at night. Interest in this is that flies generally do not possess eardrums (tympana). This genus has evolved a pair of these on its 'chest' (ventral thorax) from pre-existing chordotonal organs there, that in other species respond just to internal stretch (this reprises an earlier comment about evolutionary adaptations usually being based on pre-existing structures). The main scientific interest is that the system is seemingly far too small to work at all acoustically, because the two tympana appear to be too small and too close together to allow either a significant sound intensity difference between them, or a significant sound time delay (in humans, directional hearing works because of sound-shadowing by the head at the frequencies we resolve, which generates a sound intensity difference between the eardrums, and there's also a time delay from most positions of the sound source because of the large distance between the ears). These crickets sing dominantly at ~6 kHz (from memory) where the sound wavelength is ~60 mm, while the separation of tympana is less than 1 mm (from memory). Daniel Robert originally in Hoy's lab came up with an explanation for how it works, involving coupling between the two tympana* via some fancy chitinous rods that amplify the sound delay, such that the fly can respond to time differences (that indicate direction), in the nanosecond range. It's quite a challenging system to understand, technically. Steve (Halifax) *P.S. tympanum, eardrum (tympana = plural; Latin noun, neutral gender) = OK tympani, orchestral drums (plural only used, italian noun) = OK, but not here tympanae = hypothetical but non-existent plural Latin noun, female gender Steve (Hfx) Quoting Angus MacLean <cold_mac@hotmail.com>: > (1) Steve speaks of the caterpillar's defensive reaction to a > predator being nearby. So I'm thinking, what defensive reaction > would a caterpillar enable to avoid a wasp? ...hmm there's a leaf I > could hide under..shouldn't take me more than five mins to get > there!! However since they've evolved the detection device, there > must be more immediate steps they can take. (perhaps lay on their > back?). > > > > (2) Speaking of such things like tympanae, I read recently that > certain flies that prey on orthoptera use similar adaptations to > home in on the specific species they will parasitize. So like many > things in nature, you're dammed if you do (vocalize) & dammed if you > don't. > > Angus > > > > Date: Sun, 18 Aug 2013 18:16:28 -0300 >> Subject: Re: [NatureNS] caterpillar question- tuft control? (long, sorry) >> From: nancypdowd@gmail.com >> To: naturens@chebucto.ns.ca >> >> Thank you Steve!!!!!! >> >> That was a great explanation for the basis of