Thread by @ManuSaunders

There are some poor takes on insect extinction going around. Here’s a thread on the science behind insect extinction and the IUCN Red List, which most people use as the global standard for extinction data #insectconservation 1/...

Most of this is based on a book chapter I wrote in 2019 with @EntoProf @DavidYeates & @JenniStockan (publication delayed, out soon). We summarised the IUCN listed insects and evidence on insect threats and conservation. NB data were downloaded in April 2019

First, we need to know how the listing process works. No one is being paid FT to assess every species on Earth. Species get listed because experts had time/funding to conduct the lengthy assessment process, and because there was enough data to do the assessment in the first place

This means that there are many, many species that SHOULD be on the Red List, but are not there because:
- They don’t have a name yet
- No one has had the time/funding to assess them
- There isn’t enough data
- They are undescribed/unknown to science

Just over 8000 insect species have been assessed under the Red List process. There are at least 1,000,000 known insect species (est. 5,000,000) on Earth.
So less than 1% of known insect species have been assessed…but this doesn’t mean this handful are the only species at risk!

Many more species are considered by experts to be in danger or close to extinction, but there have been no resources available to do the surveys/assessment to make it ‘official’. Many species are recognised on national or regional lists, but have not yet been listed by the IUCN.

There are 63 insect species listed as Extinct on the Red List. This seems like a very small proportion, nothing to worry about, right?

Wrong! This is a huge underestimate of the number of modern species we have likely lost

Robert Dunn estimates at least 44,000 insect species have gone extinct in the last 600 years, calculated based on rates of extinction in birds over the same time period conbio.onlinelibrary.wiley.com/doi/full/10.11…

This more recent study estimates ~7% of species have been lost since industrial era (>70,000 species), based on extinction rates in land snails pnas.org/content/112/25…

To be listed as Extinct on the Red List, you need A LOT of time/funding. There must be “no reasonable doubt” the last individual has died. This is hard to confirm, unless there are only a few known populations and you have been following them for years portals.iucn.org/library/node/1…

The effort required to meet the IUCN Extinction criterion is nearly impossible for most insect species. Insects can be very hard to detect, because short life cycles, hard to ID to species etc. To conduct the “exhaustive surveys” the listing demands, experts need time and funding

Most insects show natural peak/trough population cycles, so you need to repeat surveys for years/decades “at appropriate times” to confirm 0 individuals. This is also why so many species were 'last seen before WW2'; this timeframe is often necessary to meet the Red List criterion

Note the "appropriate times" requirement. This is probably more important for insects than vertebrates. There's no point in surveying during autumn if your target species is only active for a few weeks during spring. If you miss one spring, you've got to wait until next year

Importantly, a species needs a name before anyone can collect data on it, or assess it for conservation status. theconversation.com/its-funny-to-n…

Thousands of species are lying in natural history museums around the world right now, collected by naturalists and scientists 10s to 100+ years ago, waiting for an expert to have the time and funding to examine and describe the species

In Australia alone, there are estimated at least 100,000 species waiting to be named theconversation.com/why-so-many-au…

This is why some extinct insect species are only known from one collected specimen, eg the Antioch katydid. By the time (~40 years) an expert examined the only known specimen in a museum drawer, the last population had gone extinct from habitat loss orthsoc.org/sina/s104lr77.…

So...63 species is very much an underestimate of how many insect species have gone extinct in the modern era. There are more that have already been lost, some are likely on the verge of extinction right now, while everyone is arguing about how many species are really at risk

Ok, let’s look at the species listed as extinct on the Red List. Here's the taxonomic breakdown at Order level:
-Lepidoptera 27
-Coleoptera 16
-Orthoptera 4
-Trichoptera 4
-Diptera 3
-Ephemeroptera 2
-Hemiptera 2
-Phasmatodea 1
-Plecoptera 1
-Blattodea 1
-Dermaptera 1
-Odonata 1

Unsurprising, as Lepidoptera and Coleoptera are the largest groups in terms of numbers and have traditionally received the most survey effort, from amateur naturalists and professional scientists. They are also more charismatic/recognisable to most people

Where were the species from?
-Oceanic islands 35
-Mainland 26
-Continental island 2
The most extinctions (45) are recorded from the USA (incl. 25 from Hawaii). Again, this probably reflects a longer history of survey effort/funding in North America.

What drove these species to extinction? For more than half (40 species) the cause is listed as unknown. Two were wiped out intentionally because they were crop pests, the rest went extinct from habitat loss or decline of a host plant

This is a snapshot of what we know most other insects around the world are facing. Habitat loss/change, overzealous pest control (esp. pesticides), and now also climate change, are major threats to insects…and to the rest of biodiversity conbio.onlinelibrary.wiley.com/doi/full/10.11…

There are hopeful stories to learn from. The Lord Howe Island stick insect was assumed extinct in the 1930s, and years of surveys had no luck. Live populations were rediscovered in 2001. It’s currently listed as Critically Endangered on the Red List abc.net.au/news/2017-06-0…

TL;DR Red Listed extinctions are an underestimate of global insect threats. They are a valuable tool for understanding what we've lost, and will keep losing, if we don’t act. We know what the major threats to biodiversity are. We know what to do to stop more species being listed