Wildlife Wednesday: Ladybug Massing

Convergent ladybird beetle ((Hippodamia convergens) massing. Photo courtesy of Ben Teton

        When going for a walk in California’s mountains, there is always the possibility of encountering something eye-catching. One of our favorite phenomena to encounter here in the Tehachapis is the great massing of ladybugs (family Coccinellidae) on stumps, logs, and rocks. These beautiful insects can be found in the hundreds or even thousands at all times of the year, but especially in the winter. Such collections can be as mysterious as they are beautiful and this week, we decided to investigate these creatures and their interesting behavior.

                First, it is important to recognize that in truth a ladybug is not just a ladybug. Technically they’re beetles, but you already knew that, right?  Being beetles, they are extremely diverse with almost 6,000 species occurring worldwide, and around 180 species recognized in California (Evans and Hogue 2006). Apparently, many of the species that now inhabit California have been introduced as biological controls for agricultural pests- a practice that has been occurring since the late 1800’s (ibid). It may be that the introduced species are now negatively affecting the natives by out-competing them for food (aphids and other soft-bodied insects).

Photo courtesy of Ben Teton

                Although there are numerous species of ladybug in California, there aren’t too many that aggregate. Here on Tejon Ranch, it appears that the convergent lady beetle (Hippodamia convergens) is the most common species to form these masses. You can tell this species by identifying the two white marks on the pronotum (the “neck” area between the wing covers and head). More specifically, these two spots are elongated and form a sort of V shape pointing towards the back of the insect. Most commonly, these groups are encountered on fallen logs at the head of major stream channels on the ranch, such as El Paso Creek.

 A quick and very non-scientific survey of Conservancy staff suggests that the most impressive masses are likely to be encountered in the late winter and spring, but smaller groups may be seen at all times of the year. Because the upper elevations of the ranch are typically inaccessible in the winter, we do not have much info on winter massing. Presumably, winter is when they are most impressive as the massing may have the effect of reducing heat loss, such as with monarch butterflies (Danaus plexippus). It is also interesting to note that many ladybugs will come up to the mountains in the summer to escape the heat. With our friend the convergent lady beetle, it seems that populations from the Central Valley go up to the Sierra Nevada, while south coastal populations inhabit the Peninsular and Transverse Ranges (Evans and Hogue, 2006). If that’s the case, we wonder where the Tehachapi beetles are coming up from!

                One interesting fact about the convergent lady beetle is that it gets parasitized by a wasp species (Dinocampus coccinellae- note that the lady bird family of beetles is called Coccinellidae, suggesting this wasp affects multiple species). While a parasitic wasp is not too much of a surprise, it’s the way they parasitize ladybugs that’s interesting. Apparently, they lay their egg on the underside of a beetle, which carries the larva around through pupation. This practice has two advantages: most obviously, it allows the larva to start eating its host. Second, it seems as though the beetle’s coloring deters predators, thus protecting the larva as well. To find out more about this interesting relationship, check out this article: http://www.sciencedaily.com/releases/2011/07/110718085229.htm.

                Another species that aggregates is the non-native multicolored Asian lady beetle (Harmonia axyridis). If you happen to notice hordes of beetles spending the winter around (or even in!) your house, it is probably this species. As annoying as their presence may be, these insects have an incredible appetite for aphids, so they’re probably doing your garden and landscape plants a huge favor by being around!

What a beautiful sight! Photo courtesy of Ben Teton

REFERENCES:


Evans, Arthur V. and Hogue, James N. 2006. Field Guide to Beetles of California. Los Angeles: University of California Press