Lepidoptera have four stages of development:
- larva (caterpillar)
- pupa (cocoon or chrysalis)
Some species will remain dormant as eggs or pupa for long periods, in order to survive winters. The longest period of their life cycle is spent in the larval stage. Most adult Lepidoptera live for only one or two weeks.
Due to their short life span, most of an adult butterfly’s focus is on reproduction. When you see an adult butterfly, it is likely in search of a mate (males) or searching for a place to lay eggs (female) or finding food to fuel its searches.
Butterflies tend to lay their eggs on or near the food plant of their caterpillar and each species has its own food preference. In the caterpillar stage, there are four or more molts of the entire outer skin with the final shedding exposing the pupa or chrysalis. While in the pupa, the caterpillar body undergoes metamorphosis and is transformed into that of an adult butterfly. When metamorphosis is complete, the pupal skin splits and the butterfly emerges, unfolds, dries its wings and then takes flight.
Both butterfly and moth caterpillars have chewing mouthparts. Caterpillars eat vegetation, mostly leaves and sometimes flowers and flower buds, while adult butterflies feed primarily on nectar from flowers. They may also feed on pollen, tree sap, rotting fruit, dung, decaying flesh, and dissolved minerals in wet sand or dirt.
The caterpillar stage is the growth stage of the life cycle and the amount a caterpillar can eat will determine the size of the adult and how many eggs can be laid. Some species are considered pests because in their larval (caterpillar) stage they can cause damage to domestic crops and trees. Some moth caterpillars will even chew holes in clothes, blankets and carpets made from natural fibres like wool, felt, silk and fur.
Do they cause problems? What role do they play in our ecosystem?
Moth caterpillars can cause significant agricultural damage. One example is the Diamondback moth larvae which feed on all plants in the Brassicaceae family. In Alberta, canola and mustard are its primary targets as well as vegetable crops such as broccoli, cabbage, cauliflower, and kale. Other examples of damaging moth larvae in Alberta include the forest tent caterpillar, the Cutworm moth, the Alfalfa Looper and the Bertha Armyworm.
A butterfly pest well known to gardeners is the Cabbage Butterfly. Its green caterpillars feed on cabbage and other related plants. Cabbage butterflies have two or three broods per year with the last brood hibernating over winter as the chrysalis and emerging in early spring.
While they do cause damage, moths and butterflies also benefit plants by pollinating flowers while feeding on nectar. Pollen collects on their feet while feeding and although they may not carry as much pollen as bees, they can transport it over greater distances and thus they aid in seed production of both wild and food crops. To attract them to your garden you need to plant host plants as well as nectar plants. Host plants are those where butterflies lay their eggs and they provide food for caterpillars. Certain species of caterpillars will only eat certain plants so that is where butterflies will lay their eggs.
Do they have predators and how do they protect themselves?
Butterflies experience predation in all life stages. Their main predators include birds, ants, spiders, and wasps. By virtue of being present on plants, caterpillars are exposed to predation from birds, wasps, and hornets. In addition, eggs and larvae are threatened by parasitoids - organisms that live in close association with their host, at the host’s expense, resulting in the death of the host. One such example is the Parasitic wasp which lays its eggs in Lepidoptera eggs or larvae. The wasp’s parasitoid larvae then devour their hosts, usually pupating inside or outside the desiccated husk.
Butterflies use a variety of means to protect themselves from predators such as chemical defences or camouflage. Chemical defences are mostly based on chemicals of plant origin. Plants have evolved such that they contain toxic substances as protection against herbivores, and butterflies in turn have evolved mechanisms to sequester these plant toxins and use them instead in their own defence. These defence mechanisms are then advertised by way of bright colours in unpalatable butterflies. One common example is the Monarch, which is poisonous to birds and other predators in the caterpillar and adult phases. The Monarch's colouration is often mimicked by other butterflies, such as the Viceroy which looks like a smaller version of the Monarch. Another defence is camouflage, where butterflies at rest can resemble dead leaves or bark and caterpillars can appear like sticks or branches. Other caterpillars resemble bird droppings or have large hairs that provide protection. Their colour helps them to blend in with host plants.
Another threat to butterflies and moths is habitat destruction, from agriculture, forestry, mining and other industrial activities and urbanization. Other threats of varying severity are pesticide use, pollution, artificial lighting, climate change and the spread of non-native species. Despite the damage they can cause, the decline of moth and butterfly populations should be of concern as they are an important food source for many other species.