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A frog insect – really?

Adult male frog-legged leaf beetle.
Credit: Insectarium de Montréal (Thierry Boislard)
Adult male frog-legged leaf beetle.
  • Adult male frog-legged leaf beetle.
  • Adult female frog-legged leaf beetle.
  • An adult male has just left his shell.
  • Frog-legged leaf beetle shells; adults will emerge in the next few days.
A frog insect – really?

The frog-legged leaf beetle, or Sagra femorata, is an example of the many species that will be on display at the new Insectarium. This magnificent beetle,* measuring roughly three centimeters, boasts fabulous iridescent colors: blue, green, violet, with reddish and golden reflections!

Where does the frog-legged leaf beetle hail from?

The frog-legged leaf beetle inhabits the rainforests of south Asia. It lives in groups of several hundred individuals on a vine known as kudzu, whose stalk it chews at in order to feed on the sap. But the frog-legged leaf beetle doesn’t just feed on that plant, it goes through its development cycle on it: the female lays her eggs there, and these will hatch into larvae that develop inside the plant. Finally, at the last stage of their life, the larvae form a cocoon in which they’ll turn into adults: we call that process pupation. The adults emerge during the summer, and the cycle starts over.

Why does it have “frog” in its name?

The males have powerful hind legs – the source of that part of their name – but these aren’t used for jumping the way they are with frogs. In fact it’s the opposite: they seem to get in the way when the beetles move around! A number of hypotheses have been formulated by researchers: the idea, for example, that the legs may serve to attract females, or as a means of defense, because the shin part is topped by a spur. But scientists can’t come to any real agreement for the time being.

Quite a challenge for the Insectarium!

The greatest challenge waiting for us when we received our first frog-legged leaf beetle shells was to figure out what to feed them on. The problem is, kudzu, also known as Japanese arrowroot, is one of the world’s most invasive plants, for which reason its importation into Canada is prohibited. We therefore had to test quite a few plants in the same family – the legumes – and ended up feeding them successfully on the pigeon pea (Cajanus cajan). We next made a number of efforts to get the beetles to reproduce both on that plant and on the stalks and roots of similar plants, but nothing worked. The frog-legged leaf beetles spent most of their time breeding – but not an egg to be found! So we’re carrying on with our research.

A breakthrough for science

At the Insectarium de Montréal we’re studying very carefully a species that has featured relatively little in the scientific literature. Thanks to our research we’ve determined a range of data about its lifespan, its food preferences, its ability to fly, its social behavior, the proportion of each type of coloring in a population, and several other subjects. We’ve even discovered the presence of males that seem to look indistinguishable from females, having neither powerful hind legs nor a spur on the shin. This is a morphology being studied in depth with regard to its evolving features and its reproduction characteristics.

We keep dreaming!

The frog-legged leaf beetle will be presented in the Great Vivarium of the new Insectarium, an immersive space where insects will be living free. We intend to carry on studying this magnificent beetle and working on ways of showcasing it.

One thing is certain, this will be a remarkable species to display. And it will be a magnificent spectacle to see these multicolored little critters move around on the branches right in front of you!

*Beetle: an insect group with a hardened front pair of wings

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