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I found this wonderful creature in my yard (I live in the south of France) last night:

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It was about 2-3cm long, with a hard carapace and wings. It also made loud hissing noises when agitated. I am curious as to what species this is, I'm quite surprised I'd never seen it before cause the beastie is quite large and last night I found it because of the noise it was making. It was upside down and hissing like a kettle.

More than the specific species' name, I am curious as to what the large antennae are for. Does their shape and size somehow increase the beetle's sensitivity to whatever stimuli these are tuned to?


Alan Boyd's comment below helped me along a bit. I seem to have found a close relative of the ten-lined June beetle (Polyphylla decemlineata) pictured below (image source)

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My guess is some kind of chafer. The elaborate antennae are probably an adaptation for detection of mating pheromones during nocturnal mating flights. –  Alan Boyd Jul 5 '13 at 18:23
    
@AlanBoyd thanks, that helped. –  terdon Jul 5 '13 at 19:03

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From the pattern on the elytra (hard upper wings), it looks like you might have a beautiful male Polyphylla fullo. Compare your photos with the P. fullo in this illustration, or photos on the Wikipedia page.

edit to fully respond to the comments:

I suspect you're right that the antennae plates in your picture are just tightly closed up, giving a different appearance. Here's a photo I took of a related species where you can see both appearances of the antennae.

And I think that Alan Boyd is correct about the antennae being used as chemoreceptors to locate females. The wikipedia page on the Ten-Lined June Bug also mentions both of these points.

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It is indeed a beautiful specimen. –  user3795 Jul 6 '13 at 13:16
    
Ah yes, I think you nailed it. That does indeed seem to be it. However, whereas the specimen I saw seems to have solid antennae, other photographs (e.g. here) show a kind of brush or duster like arrangement of what looks like separate filaments. Is that the same antenna that can be fanned out at will, is this is male/female thing or perhaps an adult/juvenile difference? Also, could you shed some light on why the antennae are shaped as they are? –  terdon Jul 6 '13 at 13:29
    
Thank you! The second photograph is just what I needed. So these little buggers can expand their antennae at will? I guess they do so in response to pheromones, cool! –  terdon Jul 6 '13 at 16:10
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Polyphylla = 'many leaves'. This may refer to the structure of the antennae, when fully deployed. –  Alan Boyd Jul 6 '13 at 17:19
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It's likely the this structure (the 'many leaves') is adaptive because of increased surface area / volume ratio. The more the 'frilly' your antennae are, the greater the surface area, which means more contact between the pheromones in the air and your chemosensory bits. –  Oreotrephes Jul 6 '13 at 22:54

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