Invertebrate biomass

Biomass should be assessed at the Order level as a minimum, allowing trends for different groups to be followed.

Biomass can be calculated as:

• Dry biomass – can be influenced by preservation liquid/storage time
• Fresh biomass – requires live trapping
• Estimated fresh biomass using size-weight models (see allometric equations for carabids below)
• Biomass of drained trap contents (e.g. pitfall trap contents drained on filter paper before weighing)

Recommendations on standardised monitoring approaches for multiple methods and collection of relevant metadata are given in Montgomery et al. 2021:
Malaise trapping (adult semi-aquatic insects, non-lepidopteran pollinators, flies)

• The Global Malaise Program is developing a malaise trapping network
• Trapping should be carried out for a defined period each year
• The placement of the trap and surrounding habitat will determine the efficacy of the trapping, so multiple traps in different microhabitats within a site are recommended
• Malaise trapping generates large numbers of individuals, requiring a large investment of ID time

Pitfall trapping (ground-dwelling beetles, ants)

• For independent samples traps should be placed 25 m apart (other studies have suggested that 10m is sufficient)
• Roofs over the pitfall traps prevent rain from diluting the samples
• See Environmental Change Network (ECN) Ground Predators protocol and Species diversity

Light trapping (adult semi-aquatic insects, ground-dwelling beetles, night-active moths, flies)

• Insects are usually attracted from within 30 m of the trap
• Microhabitat will determine the insects collected in the trap
• Post-processing can be high, as high diversity and abundance of insects are often caught
• See ECN Moths protocol and Species diversity

Pan trapping (non-lepidopteran pollinators, flies)

• See UK Pollinator Monitoring Scheme (UKPoMS) and Pollination
• UKPoMS places 1 trap per square km, which is suitable for sampling across large geographic areas
• The Bee Inventory Plot (USA) places 15 traps in an “X” with traps spaced 5m apart

Beating sheet (leaf-chewing larvae, ants)

• A square sheet 90 x 90 cm is used to catch insects that are knocked out of shrubs, trees, and, in some cases, ground cover
• Some evidence suggests that three plants of the same species must be sampled to accurately estimate insect abundance

Audio (singing insects)

• Topography, habitat and the noise of other animals can influence the recording of invertebrate activit
• Automated identification pipelines will be crucial to scaling acoustic monitoring

Active visual surveys (adult semi-aquatic insects, non-lepidopteran pollinators, leaf-chewing larvae, dragonflies and damselflies, ants, butterflies)

• Transects, point counts and area counts, the UK Butterfly Monitoring Scheme (UKBMS) is an example of a transect survey.
• Visual surveys are only suitable for large easily identifiable invertebrates

UKPoMS

• Site visits 4 times a year (mid-April to mid-May, June, July, Aug to mid-Sept)during suitable weather conditions
• Pan traps are set for 6 hours during 0900-1700
• 3 traps (UV blue, yellow, white) are set up in 5 locations per km square
• In short vegetation traps are placed on the ground, in vegetation >10 cm traps are supported on a stake
• Traps are filled with water with a few drops of washing up liquid added
• Local flower abundance is also recorded in the area surrounding the pan traps
• Flower visitation in 50 x 50 cm is also recorded

UK Butterfly Monitoring Scheme (UKBMS)

• Number and variety of species monitored
• Transects take 45-60 minutes to walk and should be 1-2 km length
• The transect represents the habitat variability within a site
• The transect is divided into 15 sections and the habitat or management type in each is recorded
• Butterflies 2.5 m either side of the transect and 5 m ahead are recorded

ECN Ground Predators

• 3 transects with 10 pitfall traps spaced 10 m apart
• 7.5 cm diameter and 10 cm deep cups to make traps, covered with a chickenwire cage to stop small mammals from falling in and a plastic rain cover
• Traps set out in first week of May, emptied fortnightly for 13 sampling periods until end of November

Allometric equations convert carabid body length to biomass (Weiss and Linde 2022)

• For carabids with body length <11.8 mm use Booij et al. 1994: ln(weight[g]) = -8.92804283 + 2.5554921*ln(size[mm])
• For carabids with body length >11.8 mm use Szysko 1983: log(weight[mg]) = -1.3 + 2.95*log(size[mm])