Orchids that Attack

How many growers know of an orchid that attacks? There is one, well quite a few in fact! Give up. Here’s a hint. It can fire its pollinarium up to about a metre, but usually just attacks unfortunate bees. Any idea? Well, it’s orchids in the genus Catasetum (pronounced kat-uh-SEE-tum). This orchid is famous for attacking insects with its pollen. I don’t know of any other orchid genus which actually attack insects. Many other deceive insects into mating with the flower, some contain hinges which swing insects into contact with the pollinarium and some even close their labellum trapping the insect inside for a short time, but the Catasetum actually goes one better and actively attacks insects.

There are between 50 and 150 species in this strange genus, depending on which expert you believe. This genus is not commonly grown in Brisbane, but you see a few examples of these orchids at the shows. They are fairly easy to grow in conditions similar to Cattleyas, although as usual, you should research each individual species as conditions do vary between species. This genus is deciduous in that they drop their leaves and remain dormant throughout winter. As with any deciduous orchid, they should be kept quite dry during the dormant period.

Catasetums are a bit of an anomaly in the orchid world for a couple of reasons. Firstly, there are male and female flowers. A Catasetum can produce male or female flowers, but usually have all flowers of the one sex in a flowering. Occasionally you will get hermaphroditic (bisexual) flowers mixed in with the normal single sex flowers. The male flowers are the larger more showy flowers, while the female flowers are smaller and much less showy. In addition, the female flower lips are always nonresupinate (held uppermost) while the male flowers are almost always lowermost, as with most orchids. Surprising, female flowers are very similar in all Catasetum species, while the male flowers show large variation across the various Catasetum species. Female flowers tend to occur when the orchid has very high light levels, while the male flowers tend to develop in lower levels of light. As the male flowers are much more desirable, growers tend to reduce the light levels during the formation of flowers to ensure male flowers are produced.

The second, even more striking aspect of Catasetums, is that they explosively attack insects. Catasetums have developed an amazing system of pollination using insects to carry the pollen from the male flower to the female flower on another orchid plant. The male and female orchid flower produces fragrances extremely attractive to a particular type of insect, usually a specific bee, and always a male bee. Each Catasetum species has adapted to suit a particular insect and no other.

Even though an insect has been attacked in a male flower, the attraction of the flower fragrance will however, attract it to the female flower, as it is totally different in appearance to the male flower. The female flower is constructed with the lip uppermost such that the insect visiting the flower must enter upside down placing the pollinarium in the correct position on the stigmatic cavity. The stigmatic cavity is extremely sticky, so when the insect backs out from the flower (which it must do due to the small size of the female flower), the pollinarium breaks from its sticky disk securing it to the insect and is left in the stigmatic cavity. This completes the pollination cycle.

That pollination ever occurs is a miracle. An insect of exactly the correct size must visit the male flower, position itself in the correct position and trigger the pollinarium which must land and stick in exactly the correct position such that the insect can still fly and also be in the correct position to pollinate the female flower. The insect must then fly off to locate and visit a female flower in the next couple of days. The insect must enter the flower in the correct upside down position and deposit the pollinarium in the correct position on exit. If all this occurs correctly, the pollination is completed, a seedpod will form, ripen, disperse the seed which hopefully lands on suitable locations such that some new Catasetums will grow.

The chance of all this going to plan must be extremely low, but as is evident by the existence of Catasetum species, must occur regularly. Makes you think, doesn’t it. Anyone feel like buying a Golden Casket ticket now?