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Boys and Girls – Sexual Dimorphism in Lubbers

3 May
A small male and large female grasshopper of the same species.

Sexually dimorphic male and female grasshoppers mate.

Found this mating pair at a field site in Argentina.  We saw these guys all over.  The females of this species are huge for grasshoppers, palm-sized and heavy.  The littler male looks a bit ridiculous perched on top. My labmate Paul calls these guys the ‘chubby chasers.’

This male and female  Staleochlora exhibit a strong example of sexual dimorphism: the adult female is much larger than the adult male of the same species.  This is common in insects, where the female’s large body size allows her to hold more eggs internally.  Cut a female grasshopper open and you will see she is literally stuffed with eggs up to her thorax.  In lubber grasshoppers (family Romaleidae) adults are often so large they can no feasibly support flight, and the wings are reduced.  For this reason they are considered ‘landlubbers.’  This male lubber can still fly fairly well to seek a mate and avoid predators, but the female must rely on her cryptic coloration and limited jumping ability to avoid becoming a meal.

My mother always asks me why entomologists are so found of ‘bug sex’ pictures.  (I got her an insect field guide and many of the photos resemble the one above.)  Aside from the somewhat warped humor value of shots like the one above (well I think it’s funny) pictures like this also provide a handy side by side comparison of males an females.  Such a reference is especially important when insects are highly sexually dimorphic.  Encountered separately, the casual observer (such as myself, unaided by grasshopper specialist Paul) would probably assume the two insects above were completely different species.

Of course, a secondary reason for the abundance of photos is that mating insects are generally fairly slow and less prone to jumping away from looming camera lenses.

Palm sized female grasshopper.

Palm sized female grasshopper.