Earth Notes: Convergent Lady Beetles

Nov 7, 2018

High on mountaintops in the fall, a curious gathering of insects occurs. Most people recognize them as the familiar ladybug or lady beetle.

Convergent lady beetles
Credit Gary Alpert

In this part of the world, they’re specifically the convergent lady beetle, the name referring to two white lines that join behind the head.  

Overall, the adults are bright orange in color, presenting a dire warning to birds and other predators that they possess an obnoxious chemical defense. If attacked, these beetles release a sticky, foul-tasting, toxic fluid from their leg joints, called reflex bleeding.  

This time of year, lady beetles gather by the thousands at the summit of Bill Williams Mountain near Williams, Arizona, and elsewhere on mountain tops and along lakeshores throughout North and South America. 

The habit of clustering in large numbers in the open reinforces their startling coloration. Also, while in these groups they enter diapause, a period of suspended animation that helps them weather unfavorable environmental conditions. 

Gardeners value lady beetles for their ability to control aphid pests. In the spring, female lady beetles lay hundreds of eggs near aphids. Beetle larvae, which look like miniature crocodiles, can consume fifty aphids a day on average, while adult beetles may feed on upwards of twenty aphids a day.

Of all insects that people encounter, lady beetles are high on the list for conjuring pleasant memories. Many cultures consider them a symbol of good luck – though it’s wise to heed the nursery rhyme and let the ladybugs “fly away home” rather than squash them and be subjected to their distasteful smell.