A Students Guide to Butterflies
Butterflies are insects. By definition, all insects posses six legs and three body segments: head, thorax and abdomen. In both of the active stages of a butterfly's life cycle, the larvae and adult, these traits can be observed. Butterflies have a complex life cycle consisting of four different stages, each with completely different appearances and durations of time. Although each species of butterfly has a different length of time in which it lives, all have the same four stages of growth: egg, larvae, pupa, and adult. The average length of time that a butterfly lives (including all four stages) is about three months. As adults, most butterflies live around one month's time.
Adult Butterfly Anatomy
I) Head
The three most salient features of the head are the antennae, the eyes and the proboscis. The antennae are used for balance in flight and olefactory sensation. Butterflies possess fragile wings. The wings can wear easily through normal use. They can also be badly damaged by predators which when attacking the butterfly grab only the wing rather than the body. Despite the loss of even the majority of their wing surface area, a butterfly will continue to be able to fly and navigate. They can do this because of the sense of balance afforded them by their antennae.
The antennae are also useful for smell. Female butterflies release pheromones (like a perfume) into the air. The male butterflies of many species can detect the pheromones from as far away as 2 kilometers (over a mile). Depending on the concentration of the pheromones, the male will be able to find the female to mate with her. It's worth noting that some species of moths are sensitive to the presence of the females' pheromones up to five kilometers (about three miles) distance.
The eyes of butterflies are large spherical structures. These are compound eyes consisting of thousands of hexagonal shaped omatidea. Each omatidea, or minuscule sensor, is directed at a slightly different angle from the others. Collectively they are directed in every direction-up, down, forwards, backwards, left and right. Because of this, butterflies are able to see in virtually every direction simultaneously.
There is a price to pay for having an exceedingly small brain and omni-vision. Butterflies cannot focus their vision as what they see is at best a blur. Furthermore, they are sensitive to only the three most basic features of vision which would be light, color and motion. Butterflies can distinguish night from day. They might distinguish color along a very narrow band of the light spectrum. Hence a butterfly might see and feed from the nectar of a purple flower but be oblivious to the red flower nearby. Butterflies are also sensitive to movement. When you try to catch a butterfly with your hand, it won't think, Here comes Billie's hand. It would however be aware that something big out there is moving, getting closer and it's time to fly.
Butterflies do not have teeth or mandibles. Rather, their feeding mechanism is a long double barreled tube called a proboscis. Because they feed through what is essentially a double barreled straw, butterfly diets are exclusively liquids. The preferred diets will vary considerably depending upon the butterfly species. While people generally think of butterflies as feeding from the nectar of flowers, other common diets include fruits, mud, cow dung, water and tree sap.
II) Thorax
The thorax, the middle body segment, connects the butterflies' appendages-the six legs and four wings. The butterflies' ears, tight membranes similar to a human eardrum are also located here. Though it cannot be seen, these membranes have hairs just under them. When a sound wave hits the membrane, the membrane vibrates and touches these hairs. When stimulated, the hairs send a message to the brain indicating the direction and distance of the sound from the individual.
III) Abdomen
The reproductive, circulatory, respiratory and digestive systems are located in the abdomen. Since liquids are the only substances that enter the butterfly's body, only liquids are excreted. The anus is located at the end of the abdomen and is generally well concealed.
A butterfly's circulatory system is relatively simple. The heart is a pump attached to a long tube that extends from the abdomen to the head. The blood is pumped through this tube and released into the tissues. Through a pressure gradient, the blood seeps through the tissue back to the abdomen. There it is sucked back into the heart and pumped forward again.
In a butterfly, there is no transportation of oxygen in the blood. Butterflies have valves called spiracles along either side of their bodies. Some of these spiracles, located mostly along the abdomen, allow oxygen to enter. Other spiracles exhale carbon dioxide. In this way oxygen will enter the body directly and once inside, there is a network of tunnels similar to the network of veins in the human body. Oxygen will travel directly to where it is needed and pass into the tissue.
The structures of the reproductive system of adult butterflies, as well as other aspects of reproduction, will be discussed extensively in the next module.
This information is provided by Evan Fitzgerald, who was an intern at The Butterfly Farm in 1999. Evan graduated from the University of New Hampshire with a Bachelor's Degree in Environmental Science in May 1998. Evan can be reached at: evan@butterflyfarm.co.cr
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