So as expected after the monstrous cold front passed with a low here on Manasota Key of 43 F on Wednesday Dec 2, a few butterflies are reappearing as the days warm up in late morning/early afternoon.
Today Dec. 4 at Cedar Pt Park in Englewood, FL, there were barred yellows and mangrove buckeyes flying around. The barred yellow is a generalist species whose caterpillars feed on legumes, a very widespread plant family. I saw two different individual mangrove buckeyes which in contrast are highly specialized for life in the mangroves. One of these was nectaring on button sage aka native lantana. This butterfly gave me two good looks with its wings open and closed. The outside of the wings is quite interesting since it is superbly camouflaged, whereas the inside of the wings is brightly marked with large eyespots. In the mangrove buckeye (in contrast to the common buckeye) the two eyespots on the inside of the hindwings are more similar (larger is less than twice the smaller) than in the common (larger eyespot is huge compared to the smaller). Also the lighter color around the larger eyespot on the inside of the forewing is mostly dark tan in the mangrove buckeye whereas the common buckeye has a much lighter border. The general ground color of the insides of the wings is also somewhat darker in mangrove buckeyes. According to an expert I contacted several years ago, the widespread common and very localized mangrove buckeyes are only separated evolutionarily from one another for about 250,000 years (relatively recently in geologic time!).
The eyespots in buckeye butterflies are assumed to have perhaps two functions- they may slightly deter birds, lizards and spiders from attacking. But the main function is probably to deflect the pecking of a bird to the peripherally located eyespots away from the crucial body parts in the central area. Indeed you will often see buckeyes that are “older” (emerged from their pupal stage longer) with gaps along the outsides of the wings due to bird pecks near the eyespots. Maybe the birds attack the eyespots to attempt a quick kill.
As an example I show here a common buckeye from an inland location with many apparent bird pecks along the periphery of the wings, leaving the central body parts safe. You can compare this butterfly with the mangrove buckeyes to see the subtle but distinct differences in relative sizes of the two hindwing eyespots and different colors of the border around the larger eyespot in the forewing.
This is really a fascinating example of “evolution in action with the development of sibling species” before our very eyes. A new species (the mangrove buckeye) has “recently” split off from the far more widespread ancestor (the common buckeye) based on adaptations and preference for a much smaller and very different habitat (caterpillars of mangrove buckeyes eat only black mangroves). Such specialization allows the mangrove buckeye to occupy an unusual and limited habitat which otherwise would not have any buckeyes. This is a very common phenomenon among coastal animals and plants. Distinct species occur just along the coastline that are specifically adapted to the harsh and unusual conditions of life in the saline zone.