Tree Cricket Tunes

If you’ve seen the Academy’s Animal Attraction exhibit, you know that creatures will go to great lengths to attract a mate. Crickets are no different. The males play a sweet song by rubbing their wings together. The tunes not only tell the female where to look for her mate, but also a bit about him, before she even sees him.

Female crickets tend to prefer large males; scientists believe that larger males are somehow better at finding and using resources, and their size reflects their advantageous genes. Larger males make lower pitched sounds, and smaller ones have a higher pitch. Females can simply listen and gauge the size of the male.

But this doesn’t work for tree crickets. These tiny, nearly transparent and highly unusual creatures change the pitch of their song with temperature. One southern Indian species, Oecanthus henryi, sings at a squeaky high pitch of 3.6 kHz when it’s a balmy 27^°C and a deep bass 2.3 kHz at 18°C. However, no one really knew how they managed this or even why they did it—until now.

A research team, led by Natasha Mhatre, used a sophisticated technique called microscanning laser Doppler vibrometry, which can pick up tiny vibrations. The technique is so sensitive that it can detect motion smaller than atomic bond lengths. While the tree cricket’s wings vibrated with greater amplitude than that, the researchers found an unusual vibrational pattern.

“The unusual long shape of their wings has always intrigued us,” says Mhatre. “Using a method called finite element modeling, borrowed from engineering, we were able to show that geometry is key. As wings go from short to long, different vibratory modes start coming closer in frequency and amplitude and start merging with each other. “

Because they are cold-blooded, insects are highly influenced by temperature. When the temperature rises, tree crickets are more energetic, call faster and engage a higher frequency mode. Their song frequency depends on how fast the tree cricket can move its wings—not on its physical size. In this way, the tree crickets can disguise their true size (whether they do, however, remains to be seen).

The male tree crickets could be communicating something else, says Science News.

The discovery could mean that these males are saying a lot more than previously thought, and that potential mates might be listening for these notes.

The research was published yesterday in the Proceedings of the National Academy of Sciences.

Image: Natasha Mhatre