The chrysalis of the butterfly looks, close up, alien and perhaps even a little frightening. Yet it is one of the four stages of the life of a butterfly and without these bizarre looking enclosures we would not have the beauty of butterflies. There always has to be a beginning in this process and above you can see a Painted Lady caterpillar beginning the transformation.
The butterfly emerges two weeks later. The abdomen is white and still inside the shell of the chrysalis. Various silk strands from the caterpillar stage are in the upper right corner of the picture. The colorful wings seen here at the top of the picture have yet to unfurl and harden. The pupal stage (called chrysalis in the Lepidoptera) is only found in insects that can be described as holometabolous (a marvelous word if ever there was one). This is a term which is applied to any insect group that undergoes a complete metamorphosis during the transition from embryo through larva, pupa and adult (sometimes known as imago).
Chrysalids come in a variety of sizes but the shape is generally similar throughout. What is quite remarkable, of course, is the emergence of a creature so vastly different in its adult form than it was in its immature period. Here a gorgeous monarch butterfly emerges from its chrysalid.
The Monarch butterfly will soon leave the empty shell of its chrysalid (known as an exuvium) behind. Although what is left behind looks translucent in the case of the Monarch the name itself comes from the Greek – chrysos – which means gold. This came about because of the color of many chrysalids – a metallic golden sheen that must have greatly enamored the ancients.
Others, like the monarch can be a fairly standard green color – but what better than this to hide it away from other animals that might wish to make lunch out of it? This small, it can hold no fear (surely?). Imagine it one hundred times larger and it is perhaps something you would call in Ellen Ripley to deal with.
Most chrysalids are formed in the open and are attached to the surface of a plant (most often that which the caterpillar feeds upon). They spin a silky pad which acts like velcro and allows them to stay firmly attached to the plant. Something else which helps is the set of hooks – called cremaster – that they have at the tip of their abdomen and these are used as an additional ‘fixative’. The process of the caterpillar creating its chrysalis is quite amazing as you can see below.
The European Swallowtail caterpillar shown here has sensed it is time to go on towards its adult form. You can see the silky pad half way down the abdomen. The cremaster are located at its top of the abdomen. These two strategies will keep it locked on to the branch while it changes.
The chrysalis stage of the butterfly could be described, you might think, with one word – still. This is true of most butterflies where there is either little or no movement whatsoever. This is described as sessile but some butterflies pupae can move their abdominal segments. They do this to warn away predators as growth and differentiation occurs within the chrysalis. The European Swallowtail above will soon become this beautiful butterfly.
Let's take a look at another transformation. The whole process of metamorphosis has more than a little of the Ugly Duckling around it. Take for example this dull looking (some might say ugly) chrysalis.
Eclosure is the name for emergence from the pupae. The pharate (the inbetween and very short stage between pupa and imago) splits open the chrysalis and emerges – most butterflies will do this in the morning. It will soon leave behind the chrysalis case, which once abandoned is known as an exuvium.
The wings are expanded by pumping haemolymph in to the veins in its wings. Haemolymph is to butterflies what blood is to us. The wings dry out and stiffen and soon the butterfly is ready to take to the skies. The transformation from pupa to imago – which seems so sudden and remarkable – is known as metamorphosis (but the word really refers to the whole process from egg to adult). However, in the case of the Camberwell blue seen here – you can’t help but refer to the very last stage as a metamorphosis in its own right.