Monarch caterpillars head-butt each other to fight for scarce food
As milkweed supplies dwindle, the insects turn up the aggression, lab experiments show
![Monarch caterpillar](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2020/11/111720_cs_monarch_feat.jpg?fit=1030%2C580&ssl=1)
Monarch caterpillars must bulk up before forming a chrysalis. Otherwise, they’ll never make it to their final life stage: a butterfly.
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