The bignonia family includes 700 species of mostly tropical distributions. The calabash tree (Cresenctia cajeta) of South and Central America is a species of bignonia that some scientists consider anachronistic, meaning it seems out of time and place. The calabash tree produces large fruits with hard rinds that no extant native animal can crack. Thus, this species has a limited distribution because no native animal can spread its seed in their dung. However, introduced horses can bite through the rind and spread the seed. During the Pleistocene horses along with ground sloths and the mastodon-like gompotheres aided in this species dispersal. Another species of bignonia, the sausage tree (Kigela africana) of Africa produces large fruit pods that are known to be dispersed in the alimentary canals of elephants, giraffes, hippos, and baboons.
Some species in the bignonia family do occur in temperate regions. The trumpet vine (Campsis radicans) is perhaps the best known and widespread. The 2 species of catalpa trees, like the calabash tree, may be examples of anachronisms because they had limited distributions before man widely transplanted them, and they produce long seed pods that no modern animal disperses. Before European settlement the northern catalpa tree (Catalpa speciousa) was limited to the Mississippi River Valley from Arkansas north to Indiana, while the southern catalpa (Catalpa bibnonioides) ranged from southern Mississippi to western Georgia and the Florida panhandle. The limited range of both species suggests they weren’t being dispersed as readily following the end of the last Ice Age as they may have been, if the megafauna hadn’t become extinct.
Illustration of the southern catalpa. It has big showy flowers, big leaves, and long seed pods. It was probably more widespread during the Pleistocene when climatic conditions were favorable.
Proposed pre-settlement range of northern catalpa (Catalpa speciosa). It has been widely transplanted.
Proposed pre-settlement range of southern catalpa (Catalpa bignoniodes). No one knows for sure what its exact pre-settlement range was because it has been widely transplanted as an ornamental.
Between 60,000 BP-30,000 BP, forests and woodlands in southeastern North America hosted many diverse species, but the climate deteriorated rapidly after 30,000 BP, and the species rich woodlands were replaced with pine and oak dominated landscapes. Catalpa trees and other less hardy species were restricted to small refuges such as ravines that were protected from the harsher climate. When climatic conditions improved ~15,000 BP, animals such as mastodons and ground sloths were headed toward extinction and were no longer common enough to be effective dispersal agents. Catalpa trees prefer early successional moist woodlands and are intolerant of fire, ice storms, and shade. The megafauna inadvertently shaped the ideal environment for catalpa trees. The presence of megafauna reduced the intensity of fires because they consumed so much flammable material. The megafauna also maintained open sunny woodlands by grazing, browsing, and trampling. Catalpa trees thrived in these primeval rich environments during warm interglacials and interstadials, but their ranges contracted during cold stadials when low CO2 levels, drought, cold, and ice storms proved problematic for this big leaved species.
I am unaware of any genetic studies comparing northern and southern catalpa trees. All the species in the bignonia family found in North America are descended from tropical species that evolved to survive in temperate climates. Northern and southern catalpa trees likely split from a common ancestor. I’m curious whether the 2 species split early during the Pliocene ~5 million years ago when Ice Ages began to occur or if they are a recent divergence resulting from a more recent Ice Age.
The reason catalpas are called fishbait trees is because they are the sole host of the catalpa worm (Ceratomia catalpae). It’s not actually a worm but rather the caterpillar stage of a brown sphinx moth. According to fishermen who use them, catalpa worms are a fair bait, if used as is, but are an excellent bait when the head is pinched off and their body is pulled inside out.
Catalpa worm. They feed on catalpa leaves and after consuming enough food burrow into the ground and pupate. They then emerge as adult moths to mate and lay eggs which hatch into caterpillars.
A catalpa tree is a mini-ecosystem in itself. Heavy catalpa worm infestations attract a whole swarm of predators. Tiny braconid wasps insert their eggs into the caterpillars, and the wasp larva eat their way through the unfortunate caterpillars. Ants then prey on the wasp larva. Tachnid flies also parasitize catalpa worms, and a species of snout-nosed beetle preys directly on the caterpillars .
At least 1 species of braconid wasp parasitizes catalpa worms. Tachnid flies parasitize them too.
Wasp larva chewing up a catalpa worm. It’s doomed.
Catalpa worms build up a chemical compound from their diet of catalpa leaves that makes them distasteful to most species of birds, but the yellow billed cuckoo is an exception. Cuckoos enjoy a specialized diet of caterpillars, and they relish catalpa worms.
Yellow billed cuckoo (Coccyzus americanus). These birds specialize in eating caterpillars. They are supposedly common summer migrants in North America. They winter in South America. I’ve maybe seen 1 in my entire life. I may plant a catalpa tree in my yard in the hopes of attracting this bird.
Catalpa trees are resilient and regenerate leaves within the same growing season following a heavy infestation of worms that completely defoliates them. Most trees, especially older individuals, can survive repeated defoliations. This is evidence they could also have withstood having their leaves heavily browsed by mastodons and ground sloths. Catalpa seedpods were probably consumed along with their leaves in the fall and deposited in big nutritious manure piles. Man began cultivating catalpa trees as ornamentals and for fishbait in 1726. Man has replaced the megafauna as a disperal agent for catalpa trees.
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