Arum Lily Frog
Created | Updated Mar 17, 2013
Arum Lily Frog
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
This little froggy, the Arum Lily Frog, Hyperolius horstocki, is a close relative of the Painted Reed Frog, Hyperolius marmoratus. While that one likes reeds and sedges, the Arum Lily frog, as its name suggests, likes arum lilies! I feature those in the Phyto-Philes of this edition of the Post. Arum lilies are in fact not real lilies although they are monocots like true lilies. Also their ‘flowers' are not real flowers; the white surrounding spathe is actually a modified leaf that protects the central flower stalk or spadix, the yellow bit standing up in the middle, on which the actual tiny flowers grow. The Arum Lily frog can often be found hiding inside these flowers – that is to say on the inner surface of the spathe, next to the central spadix, as portrayed in my picture.
I painted my frog in such a way as to make it discernible. In reality the arum lily frog can make itself very inconspicuous by changing its colour. It can range from a putty-brown colour as in my picture to a light cream, almost white, which blends in very well with the white colour of the arum lily's spathe. Also it will tuck its hands and feet, which are tinted red or orange, underneath its body. But once tucked away inside the spathe, with its hands and feet carefully hidden and its skin turned pale cream, the little frog is almost invisible. What is more, its back and limbs often become dusted with the whitish pollen grains of the arum lily, making it blend in even better (you can see a few such grains sticking on my froggy here). It now lies in wait for any insects attracted to the flowers – when they come it gobbles them up! So the arum lily frog can have its meals come to it, wasting very little energy. At night the frogs turn darker and leave the arum lilies; being agile little things they are quite capable of actively chasing and catching their prey. So let's say the frog I painted is preparing to come out of its arum lily at the end of the day.
The bright red or orange colour on the hands, feet and inner surfaces of the limbs also has a protective function. Although the frogs are very well concealed, if it happens that a predator does manage to spot one in its flowery hideout it can quickly move out and jump away. When the limbs emerge from under the body, and when the frog leaps, the red colour is suddenly very conspicuous. But then when the frog lands it quickly tucks its limbs away again and suddenly the bright red is gone again! Should a predator be looking specifically for that bright colour it will seem to it as if the frog had suddenly disappeared. This bit of confusion can be enough to save the frog's life.
Although arum lily frogs are small, reaching 4 cm/just over an inch and a half in length, they are the largest of the South African frogs belonging to the genus Hyperolius, commonly called reed frogs. Most of these are associated with reeds, sedges and tall grasses at the edges of marshes and pans. One species is associated with the flat, floating leaves of water lilies . . . yet another misnamed plant, yet again not being a true lily. The arum lily frog's habitat is ponds and pans in Fynbos, the shrubby vegetation type that is unique to the Southwestern Cape region of South Africa. Although the arum lily itself is found much more widely than this, for some reason the arum lily frog is restricted to the southern parts of the fynbos region. The rainfall here ranges from winter rainfall in the west to year-round rainfall in the east of this frog's distribution. In these areas the arum lilies can be found growing abundantly at the margins of many water bodies. They bear flowers pretty much year-round although there is a flowering peak in summer, and so the frogs can always be fairly sure of finding hideouts. But the arum lily frog can sometimes be found away from arum lilies, in reeds and sedges like other reed frogs.
They mate at night, outside of their flowers among the stems and leaves of arum lilies and other plants. Their call is a rather harsh, high-pitched, rasping, nasal quack, repeated about twice per second. The female will choose her mate by the quality of his call and they will go down to the water's edge where she will lay her eggs and he will fertilize them. The eggs are hidden among the roots of aquatic plants. The tadpoles are quite big, growing to be as long as the adult frogs, though of course much more slender.
This frog can be considered fairly safe since there are many nature reserves over its distribution range, and the arum lilies that are so important to it are abundant in nature as well as in many gardens. It is nevertheless vulnerable to habitat destruction and the encroachment of invasive alien plants which may displace it from parts of its range.
