Tropical Butterfly House
The Proboscis and Feeding
The long slender proboscis so typical of butterflies and moths is clearly well-adapted for reaching nectar at the base of narrowly tubular flowers, though it can be used for sucking up exposed liquids. It is coiled when at rest because of its length, and when in use it has a `knee-bend' that facilitates entry to slender flower tubes. Pollen of flowers visited is conveyed involuntarily by the insect on the proboscis or head. Different species vary greatly in the length of their proboscis.
Those with a proboscis that can reach deep-seated nectar of very long-tubed flowers must have evolved with them in mutual adaptation. Such insects and the flowers they pollinate are clearly highly specialized. The tips of a proboscis are armed with numerous fine spines which are thought to be used for breaking open tissues of nectar-less flowers to release the sap.
Many of the plants in the Butterfly House have been especially chosen to provide nectar for our butterflies. A Lantana provides a food source for the Postman and Zebra butterflies. A Vinca from South Africa provides nectar for many larger swallowtail butterflies. The centre of each Vinca flower is highlighted which aids butterflies in locating the nectar. This advertising is often more pronounced under ultra-violet light as many insects can see in these wavelengths. Other small plants provide some butterflies that are not specific about which flowers they visit with food. Two other plants, the purple-flowering Buddleja and the pink-flowering Pentas are favourites of many butterflies, especially the Nymphalids. Many butterflies are unable to survive on nectar alone. They require essential salts. These are obtained from wet sand or mud with butterflies often congregating displaying a behaviour called `mudpuddling'. This is commonly done by Swallowtails, Whites and Sulphurs
Special Feeding - the genus Heliconius
A special method of feeding is adapted by the New World tropical genus, Heliconius. The insect gathers a ball of dry pollen under its head and then squirts a drop of clear liquid into it; the butterfly kneads the pollen for some hours by movement of the proboscis. The liquid now enriched with amino acids, is then sucked back into the gut. The protein-building material acquired in this manner sustains the butterfly in a much longer life than is usual and is also put into egg production. Exuded fluid contains no digestive enzymes but it is known that some pollen moistened with sugar solution releases protein and amino acids.
The otherwise clear wings are covered with minute scales that are responsible for the colours we observe. These colours can be either structural or pigmented. The iridescent or metallic structural colours result from optical effects of light reflection on minute ridges and laminate structure of the scales. Most other colours result from pigments deposited in the scales. Colour and patterning has evolved to allow species to blend with their surroundings with imitations of bark or dead leaves usually occurring on the underside of the wings so at rest a butterfly becomes virtually undetectable. Most butterflies roost in trees at night, and may tropical species roost in the same tree each night. Many individuals of the same species roost together in bunches. This behaviour can be seen to occur during the evening.
Bright upper surface colours have often evolved in males to advertise their presence to females, while black and red or black and yellow patterns often indicates a species to be distasteful to a predator.
Like many insects, butterflies and moths undergo complete metamorphosis. An egg laid on suitable plants by the female hatches into a larva or caterpillar, which feeds on leaves, however, some moth larvae feed on fruit, stems, buds or even bore into wood. As the caterpillar grows it sheds its skin (exoskeleton) (`moulting'). After a period of growth the caterpillar moults into a pupa or chrysalis. During the chrysalis stage that the larva changes into the adult. The final moult releases the adult from the pupal skin. The wings at first are shrivelled and small but body fluids are pumped into the veins for several hours until the wings expand to full size. Afterwards, they harden.Our butterflies arrive as chrysalises, which are placed in the special incubators where the young adults are born. The butterflies are bred in over 38 countries worldwide with these butterfly breeders shipping to dealers who supply exhibits around the world. None are captured from wild populations. Specimens are shipped by courier reaching their final destination within a few days. The butterfly business, worldwide is a $150,000,000 a year industry with much of the money going to butterfly farms in third world countries.
The 10 to 20 day duration of the pupal stage is sufficient to ship specimens by courier just about any where in the world. The pupae are held by Canada Customs for inspection by Agriculture Canada personnel. This ensures that no pests are inadvertantly introduced into Canada. Butterflies are released into the display greenhouse after emerging from the pupal skin. Depending upon the species they will live between one and eight weeks and several species breed in the Greenhouse.
Upon the small potted citrus plants on the east wall one will find the caterpillar of the Blue Mormon Butterfly. Each looks rather fearsome since it mimics the head of a snake. The two large eyes are actually on its back, while the actual small head is hidden underneath. An osmeterium (scent gland) will make one think twice about poking this little fellow!
The Aristolochia vine on the north wall is another good site for finding some elusive but striking black and red caterpillars of the Pipevine Swallowtail.
Many unprotected animals have during their evolution become mimics of distasteful ones that exhibit warning colouration (model species). Provided these mimics are present in numbers that are low relative to those of the species being mimiced, they too will be avoided by predators.
Plant and Animal Defenses
Plants that evolve morphological or chemical defenses (secondary metabolites) to deter herbivory, gain a selective advantage as do animals that have evolved ways of overcoming such defenses. Significant as morphological adaptations are (e.g., spines, thorns), chemical defenses are more important, and occur widely in plants. Herbivores have developed unusual methods to neutralize plant toxins and use these chemicals secondarily to their own advantage.
Oleanders, for example, have leaves that to us are poisonous but some caterpillars relish them! They are not harmed by the plant's chemical defenses and become, in turn, toxic hence inedible, to potential predators.
The black and red or black and yellow patterns often found on insects act to warn other animals of danger. These are universal patterns found in herbivores and predators, and used to advertize poisonous or noxious qualities, a strategy known as warning colouration.
Butterfly populations are regulated for the most part by wasp and fly parasitoids and predators. Tiny wasp parasitoids attack their eggs before they hatch. These wasps, often under 1 mm long, develop in the egg, killing the embyronic butterfly larva. They are often agents of choice in biological control of pest species of butterflies and moths. Other parasitoid species attack larvae, pupae and adults. Birds and other vetebrates can also exert considerable pressure on the remaining populations.