|MadSci Network: Zoology|
That is a great question to ask. I shall try my best to answer it.
If you ask about ladybugs, I guess you think about this beautiful red or orange beetles with 2 or 7 or 15 spots. While these are the best known ladybugs there are many other species around and not all of them have spots. Some have stripes, some irregular dots and some are just plain black.
But I am sure you ask about the very beautiful ones that you can find in your backyard, so let's concentrate on these.
Why do they have such colors that make it easy to spot them? Think about other animals that have such obvious coloration.
Wasps Most wasps are brown, redbrown or black and blend very well with bark and twigs from bushes. But yellow jackets have yellow and black stripes, why? Yes, the yellow jackets have a stinger, and they could sting you (or a bird, that tries to catch them)
Butterflies and moths Most butterflies and moths resemble bark, leavs, flowers and are hard to spot if they don't fly up. But among all of them the monarch is very colorful- why? The monarch has a poisenous awful tasting substance in its body, so that no bird will try to eat one a second time.
Frogs Most frogs are brown or greenish, like mud, stones or soil, so that they are hard to spot. But some frogs, the dart poison frogs, are red and blue and yellow, why? Their skin contains a very dangerous chemical, that easily can kill a bird or any other animal that tries to catch them.
You see, very often such bright and colorful animals can defend themselves very well. The colors warn you and any other animal that tries to catch them. Can it be the same with the ladybugs? Most scientists believe: yes! The ladybugs' bodies contain a bad tasting substance, that is also slightly poisonous. They also warn other animals not to try to eat them, as whoever tries will not forget the bad experience soon.
So - that is why ladybugs often have a colorful body with spots on them.
If you want more information try a search on the internet. If you use the scientific name for ladybugs that is: Coccinellidae you will find many good pages with useful information, for example, why it is good to have many ladybugs in your garden. Try this site on lady beetles as a starting point
TEACHERS' INFORMATION: Some general information first: ladybugs (also called lady beetles or ladybirds) belong to a group of beetles, that is scientifically called family Coccinellidae, with about 4000 species woldwide, more than 400 in the USA. Most of them have in common that they are covered with beautiful colored spots (but some of them are just plain black).
Why now do they usually have these spots? I have to split your question into two? 1.) Why do they have such an obvious coloration that makes them so easily visible? 2.) Why spots and not any other pattern? 1.) Animals with conspicuous markings that make it easily recognizable usually warn would-be predators that it is poisonous, foul-tasting, or dangerous. For example, the yellow-and-black striped abdomen of the wasp warns of its sting. The 12-spotted ladybird, like its relatives in other parts of the world, is poisonous. When disturbed, both the larvae and adults can force blood out through joints and other weak areas in their exoskeleton, an adaptation called "reflex bleeding". Their blood contains toxic alkaloids, and has a distinct odor that deters predators. In order that predators, particularly birds, recognize it as a poisonous species before taking a bite, ladybugs have developed bright warning coloration. Those birds that do taste these beetles are not likely to quickly forget their distinctive pattern. 2.) Obviously not all ladybugs have spots. Some are just black, others have stripes or irregular patterns. Each pattern is genetically fixed for each species, but can be influenced by environmental factors (temperature). Today it is not possible to say, why one species has red dots on a black ground, the other one black dots on red ground, and the next stripes. There are too many factors that play a role here: the defense mechanism described, but in addition for example sexual attractiveness or recognition, heat uptake (in sunshine black gets much warmer than yellow or orange), energetical costs to produce the pigments, predator pressure, behavior of the animals. As in evolutionary terms nothing is planned, the major cause is just chance. These colorations are a good working compromise for ladybugs to survive in the environment that we have today.
Science always has problems with "why?" questions as they principally can not be answered scientifically. The "why" level it is much more meaningful and satisfactorily answered on the level of belief systems: For example "God knew, we humans would like to see beautiful animals around so he created some animals very colorful."
There is lot of interest in such defense chemicals – here are just some examples of original scientific articles:
Tursch, B., J.C. Braekman, D. Daloze, C.Hootele, D. Losman, R. Karlsson, and J.M. Pasteels 1973 Chemical ecology of arthropods. VI. Adaline, a novel alkaloid from Adalia bipunctata L.(Coleoptera, Coccinellidae). Tetrahedron Letters 3, 201-202. Tursch, B., D. Daloze, J.C. Braekman, C. Hootele, A. Cravador, D. Losman and R. Karlsson 1974 Chemical ecology of arthropods. IX. Structure and absolute configuration of hippodamine and convergine, two novel alkaloids from the American ladybug Hippodamia convergens (Coleoptera - Coccinellidae). Tetrahedron Letters 5, 409-412. Holloway, G.J.; de Jong, P.W.; Brakefield, P.M. & de Vos, H. 1991 Chemical defence in ladybird beetles (Coccinellidae). I. Distribution of coccinelline and individual variation in defence in 7-spot ladybirds (Coccinella septempunctata). Chemoecology. 2, 7-14. de Jong, P.W.; Holloway, G.J.; Brakefield, P.M. & de Vos, H. 1991 Chemical defence in ladybird beetles (Coccinellidae). II. Amount of reflex fluid, the alkaloid adaline and individual variation in defence in 2-spot ladybirds (Adalia bipunctata). Chemoecology. 2, 15-19. Hope that helps Jurgen Ziesmann
Try the links in the MadSci Library for more information on Zoology.