Ladybird beetles are among the most familiar and recognizable of insects, but most people either don’t notice their larvae or don’t realize what they are when they see them. The larvae in fact are very common, spending their time crawling around on plants as they search for small insects such as aphids. Ladybird beetle larvae are often as colorful as the adults, with ferocious-looking spikes of several colors covering their bodies.
Ladybird beetle adult
The larva in this month’s photo was one of a number of larval and adult ladybird beetles that were found in our ecology lab in Fall 2002. They were feeding on aphids that had colonized the perennial ryegrass in experimental plant communities set up as part of student research projects.
Ladybird beetles are well known for their appetites for soft-bodied insects such as aphids, and they are often introduced to gardens, agricultural plantings, or greenhouses for insect control. Aphids are sap-feeding insects that can multiply rapidly when living on appropriate plant species (the many species of aphids have different food-plant preferences). Though individual aphids are tiny, there can be considerable impact from the collective feeding activities of dense populations.
Aphids on perennial ryegrass. Aphids pierce the
plants with needle-like mouthparts to suck the sap
Though ladybird beetle adults and larvae are both predaceous aphid eaters, in most insect species the majority of an insect’s feeding takes place in the juvenile stages (indeed, in some insect species such as mayflies the adults do no feeding at all). While adults need energy and resources to support basic metabolism, activity, and reproduction, the immature stages are where nearly all body growth takes place, and this requires a great deal of food. Aside from the production of eggs (or sperm), little if any growth occurs in adult insects.
Beetles have complete metamorphosis (insects with this developmental system are called holometabolous insects). Such insects go through a series of larval stages that look nothing like the adult, molting (shedding) their exoskeletons between each stage. Their exoskeletons increase in size by quantum leaps with each molt. The last larval molt produces the pupal stage during which metamorphosis to the adult body form takes place. During the pupal stage, nearly all body tissues and cells break down to a rich chemical soup. This gooey, self-digested larval body provides the building materials and fuel for the growth of a completely new body that develops rapidly from small clusters of cells that remained intact. With one more molting, the newly formed, completely remodeled adult body emerges from the pupal “skin”. After that, the insect will never molt again.
Ladybird beetle larva consuming an aphid on
a blade of grass.These larvae are voraceous aphid eaters.
Not all insects have complete metamorphosis (aphids do not, for example…immature aphids look like miniature versions of the adults), but complete metamorphosis (holometabolous development) is utilized by some of the most abundant and successful insect groups. In addition to the beetles, other holometabolous insects are flies, butterflies, moths, fleas, ants, bees, wasps, and some others.
Though adult and larval ladybird beetles exploit the same food resources, the holometabolous developmental system often allows juveniles to exploit different food resources from the adults, avoiding competition with the adults, and allowing a greater diversity of resources and niches to be exploited by the species overall. For example, most caterpillars feed on leaves, while adult butterflies and moths drink flower nectar. Larval mosquitoes feed on microorganisms filtered from the water, while adult female mosquitoes feed on blood. Corn rootworm beetle larvae feed on roots, while the adults feed on aboveground plant parts such as floral structures and leaves.
Student research project that was unintentionally colonized by aphids and ladybird beetles (this project investigated the effects of trampling on plant community structure).
When one considers that beetles are by a wide margin the most diverse group of animals on earth, and many of the other insect groups with complete metamorphosis are also quite diverse, it is quickly apparent that this seemingly strange developmental system is anything but rare. According to some estimates, the collective species diversity of just the beetles, flies, butterflies, moths, wasps, bees, and ants is around 740,000 species, with many more species yet to be discovered (Rupert, et al, 2003).
This is an enormous number, but just how big is this? To put this into perspective, consider that the beetles and other holometabolous insects make up about 80% of total insect diversity. Since the insects overall are twice as diverse as all other groups of animals combined, holometabolous insects (and especially the beetles) make up a majority of the Earth’s animal species diversity.
Holometabolous insects seem utterly bizarre from our human perspective. Indeed, self-digestion of the larval body and creation of an entirely new body from scratch seems like fantasy from a science fiction movie, and the ladybird beetle larva shown below looks like it could indeed be some sort of alien from another planet. However, holometabolous insects greatly outnumber us by any measure, be it species diversity, overall biomass, or simply sheer number of individuals. By this line of reasoning, these are actually the most ordinary of creatures. Perhaps we are the creatures who should be considered strange?
A Google search for “ladybird beetle”, “coccinellid”, or “coleoptera” yields a great abundance of links to interesting and informative web sites dealing with ladybird beetles or beetles in general. Give it a try and explore!
Here are a few with information on ladybird beetles, including diagrams and some photos of the eggs and pupae:
Ruppert, E.E., Fox, R.S., Barnes, R.D. 2003. Invertebrate Zoology: A Functional Evolutionary Approach. Thomson-Brooks/Cole, USA.