As they are on the menu of so many predators, rabbits are very vigilant, constantly on the lookout for danger. They have eyes set wide on the sides of their skull which give them a broad field of vision, and sit on their hind legs to see further. With so many enemies around, it might seem counter-intuitive for a prey animal like a rabbit to make itself more visible by having a white rump. However, the white underside of a rabbit’s stubby tail (called a scut) is not that easy to see when the rabbit is grazing or moving slowly. It’s most noticeable when the rabbit is running, probably heading away from danger. This has led to several theories why rabbits have white tails.
Firstly, it acts as a warning to other rabbits in the warren. If a rabbit senses danger it raises its tail and thumps its foot to alert other members of the warren. Rabbits are mostly active in the low light conditions of dawn and dusk so a white flash would stand out, alerting other rabbits to run. Another theory suggests that by having a white tail, predators are attracted to the ‘right’ end of the rabbit and aim for the rear instead of the head, giving the rabbit a greater chance of escaping.
Rabbits also have a strict hierarchy and there can be a lot of aggression within the colony. Males, called bucks, will fight for access to females, known as does. The most dominant buck gains mating rights while the does compete for nest sites. Fights between the females can lead to serious injuries and even death. So one theory suggests that the tails are used like a white flag in surrender, to show submission to other rabbits and avoid potentially deadly fights. Dominant rabbits tend to be caught by predators more often than those lower in the hierarchy, perhaps because they are distracted by fights or because chasing off other rabbits makes their white tails more visible.
The rabbit’s tail probably has several functions, but the costs of having a white, fluffy bottom must be outweighed by the benefits or natural selection would have led to something a bit less conspicuous.
Pitching Up
I was driving to Brecon in south Wales last week and saw several colonies of tent-making caterpillars. The colonies were all very large, a metre or so long. Some of the colonies had completely stripped the hedgerow for long stretches and all that was left was twigs and silk. Are these native to the UK (I have seen very much smaller colonies on hawthorn) or are they an invasive species? Rob
There are quite a few native species of moths and butterflies whose caterpillars make tents, such as the lackey moth (Malacosoma neustria) and marsh fritillary butterfly (Euphydryas aurinia). However, the impressive size and extent of the tents that Rob describes suggests that they were made by one of our eight species of ermine moth that belong to the genus Yponomeuta.
The adult moths are fairly inconspicuous, with white or grey wings adorned with rows of black spots and a wingspan of 15–26 millimetres, depending on the species. The caterpillars and their webs are much more noticeable, though, especially when there’s a population explosion and their numbers grow to epic proportions. This can occur when there is a lack of predators or parasites (ermine caterpillars are often parasitised by ichneumon wasps) or when weather conditions work in their favour. The caterpillars’ fleecy white tents can cover large areas of trees and hedgerows, looking like giant spider’s webs or something out of a horror film. The truth is much less sinister.
Each ermine species has a favoured host food plant on which eggs are laid and the caterpillars subsequently munch their way through. For example, the colonies that Rob saw on hawthorn were probably caterpillars of the small or orchard ermine moth (Yponomeuta padella). The adults are on the wing in June/July and the females lay clusters of eggs on their specific food plant. These hatch into tiny larvae that spend the winter burrowed into leaves or stems. They emerge in spring when the buds burst and turn into busy eating machines. A caterpillar grows quickly until it literally needs to burst out of its skin in a process called ecdysis. Once it reaches a certain size, a caterpillar sheds its skin so that it can grow into the next stage, or instar. Most moth and butterfly caterpillars go through this four or five times, and a caterpillar can grow to over a thousand times heavier than when it emerged from the egg.
Ermine moth caterpillars live in large groups and construct their characteristic tents from silk. They bind leaves together in loose webs and feed on the leaves within them or nearby. As they run out of leaves, the caterpillars extend the tents to cover new areas of tree or bush. If the caterpillars venture beyond the safety of the web, they can leave a trail of chemical pheromones to find their way back.
The tents provide protection from predators – few birds would risk getting caught up in the silken webs. The layers of silk also act as insulation, retaining heat and encouraging the caterpillars to remain huddled together. The caterpillars need warmth for their digestion to work efficiently. Once they have grown large enough, the caterpillar will pupate and transform into an adult moth.
The plants that the caterpillars feed on may be stripped of leaves. Some ermine moth caterpillars can be minor agricultural pests but generally the plants affected soon recover. After all, it wouldn’t be in the moths’ interest for the caterpillars to destroy their host plant as they will be returning as adults a few weeks later to lay their own eggs on it.
Spring Quiz
1. If you were offered a plate of wallfish, what would you be eating?
A. Crayfish
B. Wild strawberries
C. Garden snails
D. Mussels
2. Spring sees the arrival of many of our migrant birds, but which travels the furthest?
A. Swallow
B. Swift
C. Osprey
D. Arctic tern
3. Which of the following reptiles lay eggs?
A. Adder
B. Common lizard
C. Grass snake
D. Slowworm
4. A flock of goldfinches is delightfully known as a ‘charm’, but which animals gather in these more ominous-sounding groups?
A. An unkindness
B. A siege
C. A smack
D. A scream
5. If a dog is described as canine, which animal is vulpine?
A. A vole
B. A fox
C. A peregrine falcon
D. A red squirrel
6. Which iconic spring flower is also known as the Lent lily?
A. Wild daffodil
B. Primrose
C. Wild garlic
D. Bluebell
Spring Quiz Answers
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