On the Wing: Green-Veined White

After a break of a few weeks, I have decided to start a new occasional series this year on the various butterflies that I come across on walks or in my garden, and despite the late spring and bad breeding season last year a few have finally started to show up. I will start off with a very pretty little butterfly that is often mistaken for one of its relatives, the Green-Veined White Pieris napi. Although much the same size as the cabbage pest the Small White, it can be distinguished by the heavy green veining on the underside of the hind wings.

At their best now: Camellias

This year, as various interesting plants in the zoos gardens come into their best season, I will be writing posts on their natural (and garden) history. Kicking off the series, our Camellia Walk (between Twilight World and the Reptile House) has several large and old Camellias in full blossom. They started some weeks ago, but the cold spring has held them back.

New Arrivals: Upside-Down Jellyfish

Adult Cassiopea

Now on show in the marine invertebrate section of Bug World is a small group of unusual jellyfish, the Upside-Down Jellyfish Cassiopea sp. As you might guess from their name, these creatures spend their adult lives resting upside down on the sea bottom, instead of swimming in the supper surfaces of the sea as most jellyfish do although if disturbed they can swim with contractions of the bell as with their more mobile relatives.


Cassiopea is only found in shallow waters with high light levels on the sea floor, usually lagoons, mud flats and mangrove swamps. They do this because like corals they harbour algae in their tissues, which provide food to their host by photosynthesis. As well as their algae, they can also feed on smaller organisms as they retain the nematocysts, the stinging cells which predatory jellyfish use to kill prey, although to humans at least the sting is very weak. The group of jellyfish they belong too has modified their internal anatomy – the primary mouth at the center of the bell is closed and instead secondary openings into the digestive cavity open at the edge of the body.

A different morph - colour is due to symbiotic algae

Jellyfish (Scyphozoa is the technical name) exhibit alternation of generations during their life cycle. The adult reproductive phase is called the medusa, and the adults are either rmale or female. Eggs and sperm cells are released into the digestive cavity and expelled through the mouths into the surrounding water, where they meet and the egg is fertilised. After spending a short period in the plankton, the egg become a planula larva (so called because it resembles a planarian flatworm) only a few millimetres long, which settles on a suitable substrate to become a polyp with tentacles that feeds and grows for a few months. How the planula selects a suitable substrate is not entirely clear – in the Bermudan species C. xamachana they seem to prefer the shady side of decaying Red Mangrove leaves. Presumably other species (the genus is found worldwide) have similar requirements, but I have not seen much study of differences between them. At this point they also acquire their symbiotic algae through feeding on plankton.

Lateral view showing the feeding arms

After growing for a few months, the small polyp begins to strobilate. This involves budding off tiny medusae, which then settle down on the sea floor to grow into the adult phase over the next few months. As neither the adults nor the polyps are especially mobile, how many actual species of Cassiopea exist is subject to debate and is probably more than are currently recognised – they certainly seem to come in different colour morphs in parts of their range but whether these are actually separate species is unclear. They do not seem to have many natural enemies – possible specialised flatworms prey on them as they do on corals, but I have not found any specific documentation on line on these. None of the forms is currently listed as threatened, and this is unlikely to change in the near future.

(images from wikipedia)

Beetles and Bugs 6: Spot the difference

P.biguttatus

People often use the term ‘bug’ to mean any insect (except possibly butterflies) but the true bugs belong to the order Hemiptera and are one of the most diverse groups of insects. Although often confused with beetles, most of which are of similar size, they can be distinguished by their distinctive wings and mouthparts which are designed to suck liquids – either of plant or animal origin depending on the species concerned – and most of all by their totally different life cycle.

Beetles and Bugs 5: Lesser Goliath Beetle

M.polyphemus male

Now on show in the newly redecorated Bug World is a pair of Lesser Goliath Beetles Chelorrhina polyphemus. The generic name is a bit uncertain – some authorities now put them in Mecynorrhina. A Cetoniine scarab beetle, they originate from Central Africa rainforest and have a very similar life cycle to the Purple Jewel beetles and Hercules beetles I wrote about in earlier posts.


One of the larger scarab beetles, males of this species can reach nearly 8 cm long, with females around 4cm maximum. Aside from size, the males can be distinguished by the ‘antlers’ on the head, which are not as well developed as those of the Rhinoceros beetle but are still useful in fighting with other males, for which reason males need to be kept separately in captivity.

M.polyphemus female

The adults can live many months, and the complete life cycle from egg to death of adult is around a year, although development time for the larvae is shorter at higher temperatures. Eggs are laid in the soil after the female digs down deep into the substrate, and the larvae feed on decomposing wood, decaying leaves, and anything else with some nutrient content. Although not predatory, they could be cannibalistic if hungry and crowded, and to protect themselves they craft a quite solid cocoon incorporating wood particles before pupating.

Although brightly coloured, the metallic green of their wings is quite effective camouflage amongst rainforest foliage. They are not especially secretive, instead relying on their wings (they are good fliers) and well-armoured bodies to protect themselves. Large beetles like these do not have many predators as adults, although the larvae are favoured foods for many terrestrial mammals and reptiles, and their main threat is probably parasitic wasps, many of which are species-specific, although I have not been able to find much information on what parasitizes this particular species.

In captivity they are slightly harder to raise than the smaller species, but are well within the range of a home hobbyist. Basic rearing conditions are a suitably large container of rotting wood and dead leaves maintained at around 25 degrees for the larvae, supplemented with dry dog food to add nutrients. Adults feed on fruit such as banana, but need a covered container to prevent escape.

For more on raising these and other beetles, see here: http://www.bugnation.co.uk/viewforum.php?f=272

(images from wikipedia)