28 December 2007

Ladybugs galore


I photographed these ladybugs at an altitude of 2500 m just below the summit of Honaz Mountain in central-western Turkey on 5 July 2006. Although the summer was supposed to have arrived, it was a cool and rainy morning.

We were overturning the limestone rocks to look for snails and kept finding clusters of ladybugs under them.


What were the ladybugs doing under the rocks on top of the mountain? A similar question was asked a while ago by a New Scientist reader, who had witnessed a similar phenomenon at the peak of Mount Etna, and the 3 answers sent in by other readers got published in the The last word page of the 1 December issue. The answers are (1) the ladybugs had landed on the mountain during their biannual (fall and spring) migration between Europe and north Africa; (2) they were hibernating (the reader who asked the question, however, did not indicate the season when the observation had been made); (3) the ladybugs had been brought to the peak by currents of warm air flowing up from the lower slopes.

The clustering of ladybugs is a commonly encountered phenomenon not restricted to Europe. For example, in the Common Insects of North America (1972), Swan & Papp wrote this about the convergent lady beetle (Hippodamia convergens):

Hibernates as adult under stones, bark, or litter. In the western states, particularly along the Sierra Nevada Mts. and Coast Range of California, great swarms of them fly to the mountain canyons in late fall to hibernate, and congregate in huge aggregations under the leaves and snow, returning to the broad valleys below in early spring.

Which of the 3 possibilities offered by the New Scientist readers best explains the ladybugs we found on Honaz Mountain? I am ruling out the migration hypothesis, because July seems a bit too late for them to have been migrating, presumably, from the Middle East or northeast Africa to Anatolia or further up to eastern Europe. Involuntary transfer by warm currents creates its own question: how do the bugs ever get down to the lower altitudes? When the air is cooler? If that's the case, then these ladybugs shouldn't have been where we found them on that cool morning. That leaves the possibility that they were still hibernating in the beginning of July, which is not very plausible either. The spring had already come and gone at lower altitudes.

One other possibility is that the bugs may spend their entire lives where we found them near the peak of the mountain. When it is cold and/or rainy, they may cluster under the rocks, because there is no other shelter for them at that altitude. However, the problem with that scenario is that both adults and larvae of ladybugs are predaceous, but I doubt it very much that there would be enough prey on that bleak mountain top for so many of them to survive.

What were the ladybugs doing under the rocks on top of the mountain?


umit said...

I faintly remember talking about this. I have seen photographs of same event occurring in same heights of a different mountains in S Turkey. Some cephalopods aggregate during coupling and before dying, spiny lobsters migrate in aggregations. I thing this can be understood in the context of aggregation.

Why do insects aggregate? Why not others but this species (and few others) of ladybug? Lastly, why top of the mountain? These are questions to answer.

All are the same species and adults. I think this is a sufficient detail to think about migration or breeding.

Thay may be simply stting closer to enhance their supercooling abilities in cold and rainy days. But why they are up on the mountain? I cant say anything logical about it.

Anonymous said...

I wonder if this has something to do with a peculiar ladybug habit. If you ever have one on your finger, arm, stick, etc., they alway walk up to the topmost point they can find, and then fly. Is there some habit/instinct of ladybugs that makes them go upwards. As strange as this seems it would be a powerful mating ability as they could all conglomerate during certain periods of the year.

It seems like a stretch to take a micro example of the ladybug on a finger and extrapolate it to mountaintops, and perhaps this is a much wider behavior, but I though I would point out the connection.

BLT said...