Bugs on the bayou (part two) – butterflies, termites and ants.
Editor’s note: This is the second part of a three part post on some of my thoughts on the theoretical importance of insects in the Mississippi River delta. If you haven’t read part one you should do that now.
I fortuitously discovered the above spectacular radar image of ‘ground clutter,’ resulting from millions of birds migrating across the Mississippi River delta. A radar image from SW Louisiana (below) shows that all of south Louisiana is critical to bird migration.
Imagine the biomass of coastal insects required to feed such enormous flocks of hungry migrating insectivores. This is one dramatic piece of evidence that coastal bugs are universally critical – and important barometers of coastal ecosystem health.
I originally conceived of this post as being limited to three functionally important groups of insects (termites, ants and mosquitoes). Butterflies were added as an afterthought, partly because their larval stages are important both as herbivores and prey in coastal marshes and swampforests, but also because adult butterflies have mesmerized humans and been given a mystical esthetic status throughout at least the 5+ millennia of recorded history.
The order in which these groups are discussed relates to their trophic level, from herbivores and cellulose eaters (butterflies and termites) to predators (ants) to highly specialized parasites (mosquitoes). The biomass of these broad groups declines with their trophic “distance” from solar energy, with herbivores and detritivores (primary consumers) being most abundant and parasites having the lowest bimass (see graphic).
Monarch butterlies exist over much of the world, including Australia, Europe, Asia and the Western Hemisphere. What is extraordinary, however, is that the entire New World population of this species completes an annual 4,000 mile round trip migration from Mexico through Texas and Louisiana into Canada and back again – a trip that involves four generations. This migration is said to be absolutely unique throughout the animal kingdom. See map on the left.
I previously called attention to the curious apparent disinterest in insects by coastal ecologists. The exception that best proves this rule is Edward Osborne (EO) Wilson, the famously brilliant and prolific ecologist and evolutionist who since childhood has recognized the functional significance of insects, especially social insects. Here’s a wonderful quote by Wilson and his co-author Bert Holldobler in a 2005 treatise on insect evolution.
Humanity lives in a world largely filled by prokaryotes, fungi, flowering plants, nematode worms, spiders, mites, and six ecological keystone insect groups: termites, hemipteran “true” bugs, phytophagan beetles, cyclorraphan flies, glossatan moths, and hymenopterans, the last comprising bees, wasps— and ants.
As stated in the first part of my post on coastal bugs I arbitrarily selected three groups to represent the potential impact of insects in south Louisiana: termites, ants and mosquitoes. My arbitrary decision was vindicated when I discovered that EO Wilson lists termites and ants as two of six keystone groups of insects.
Termites are descendants of perhaps the least popular insect group on Earth, the cockroaches. Here’s a quote that explains the relationship:
…one of the most interesting aspects of cockroach classification is that of Termites now being thought of as a family of eusocial (living together in a colony with only some individuals being able to reproduce) cockroaches. Termites were previously thought to be a separate order (Isoptera) of their own.
The following quotes are taken from the web page of Dr. Sai Bhaskar Reddy Nakka, an agronomy specialist (with an interest in climate change). In marked contrast to ecosystem ecologists such as EO Wilson, Nakka describes termites in anthropocentric and pejorative terms. For example he notes that they cause enormous economic damage to human-built structures. I bolded some words and phrases that are non-scientific, subjective or anthropocentric.
The total weight of all the termites on Earth is estimated to be much greater than the total weight of all the humans on Earth. There are some 4 billion tons of them. It is said that about 700 kg of termites exist for every human on the planet. In terms of carbon churn and methane they contribute the most as compared to other living species on earth. They eat everything cellulose, often even living plant tissues. Termites annually consume food on an average rate of seven times of their own biomass.
…The type of plants that do manage to survive in termite areas are those which devote a great deal of energy to producing anti termite toxins. Acacias and all types of magnificent mahogany tress all derive from the selective pressure to avoid being gobbled up by termites.
The point is that not everything natural is necessarily good and wholesome, just because termites have been degrading their environment for hundreds of millions of years does not mean that their influence is desirable. Termites do not like the cold. If they did, perhaps the soils of the temperate zones would be as poor as tropical soils. The biomass per sq km of termites is often far greater than any other animal. Termites cause more damage to homes than fires and all storms combined in the USA. Homeowners insurance doesn’t provide protection from the perils of termites. Termites cause damage to more than 600,000 U.S. homes with losses totaling over $2 billion annually.
There are some 4 billion tons of them. It is said that about 700 kg of termites exist for every human on the planet. In terms of carbon churn and methane they contribute the most as compared to other living species on earth. They eat everything cellulose, often even living plant tissues.
Much of EO Wilson’s reputation has been earned by an amazing lifetime body of research on ants. In terms of the global significance of ants consider this quote by a less familiar ant researcher named Ted Schultz from a 2000 paper entitled In search of ant ancestors from the Proceedings of the National Academy of Sciences:
Ants are arguably the greatest success story in the history of terrestrial metazoa. On average, ants monopolize 15-20% of the terrestrial animal biomass, and in tropical regions where ants are especially abundant, they monopolize 25% or more.
And another ant quote from a 1990 paper by Holldobler and Wilson:
Ants are especially notable among the insects for their ecological dominance as predators, scavengers, and indirect herbivores. Although the 11,000? species of the ant family (Formicidae) make up <2% of the known global insect fauna, they compose at least one-third of its biomass. In the Brazilian Amazon, as judged by one survey, the biomass of ants is approximately four times greater than that of all of the land vertebrates (mammals, birds, reptiles, and amphibians) combined.
Note two points: (1) according to Wilson and Holldobler, ants comprise at least one-third of the total global insect biomass; and (2) ant biomass equals four times that of all terrestrial vertebrates combined. Compare the above passage with ant quotes from Christopher Lloyd’s book What on Earth evolved? 100 species that changed the world. Lloyd very likely derived his information from Wilson’s research.
Ants dominate life in the soil on virtually every continent except for frozen Antarctica. Only Iceland, Greenland and a few Pacific islands have no indigenous species. In many ecosystems, especially in the tropics, up to 20% of the mass of all land living creatures can be accounted for by the ants alone, putting them at the top of today’s list of nature’s most populous living creatures.
Fossils of ants trapped in amber date back to the mid-Cretaceous Period (c. 120 million years ago) but it was only after the demise of the dinosaurs (65.5 million years ago) that ants spread in significant numbers. About 14,000 different species have been identified to date.
In light of Lloyd’s description of the ants I am struck that he ranked them only 14th in global importance.
Energetic impact of ants and termites
On a unit weight basis the amount of food energy consumed by an individual animal is inversely proportional to its size. That’s because small animals – such as insects – have much more surface area than big ones and they tend to have higher metabolic rates. A ton of mice would consume considerably more grain per year than a ton of elephant. Energy consumed by the total population of an animal within an ecosystem is a function of its trophic level, its metabolism and its biomass (see trophic pyramid above).
The biomass estimates of termites and ants seem to primarily come from tropical regions so I would expect somewhat lower population densities in subtropical south Louisiana because of cooler winter temperatures and rare cold snaps. Just imagine how much of the total terrestrial primary production in south Louisiana is consumed by termites.
Granted, much of the information presented on ants and termites are extremely crude and not specifically related to the Mississippi River delta. Nevertheless, I would argue that for ants, termites (and all insect orders) south Louisiana offers an incredibly friendly landscape on which to flourish, given the humid subtropical setting, long growing season, mild winters, lush vegetation and high primary production, organic soils, and abundant prey.
Part three of Bugs on the Bayou will be posted on February 1: primarily on mosquitoes!
Len Bahr (firstname.lastname@example.org)