Wildlife - Invertebrate Surveys


Planning a Survey

  • When planning an invertebrate survey, you need to consider a number of factors:
    • which invertebrates?
      • about 35,000,000 invert types
    • which microhabitats?
    • weather conditions
      • inverts are ectothermic
    • time of day
    • time of year
      • during the winter and autumn, there tends to be a decrease in activity
    • temporarily storing live inverts
    • killing and preserving inverts
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Which inverts?

  • the inverts are a huge group, with many diverse smaller groups from nematodes (roundworms) and annelids (segmented worms) through to molluscs (slugs and snails) to crustaceans (such as woodlice), centipedes, spiders, and insects.
  • worldwide there are over 1 million species of insects grouped into around 25 'orders'
    • for example, dragonflies, grasshoppers, beetles, and bees
  • different groups have different habits and flying insects will require different trapping methods
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Which microhabitats?

  • mostly live in very specialised habitat types
    • the bark of different tree and shrub species
    • leaves of a specific tree
  • when you are surveying a particular site you will probably need to sample a wide range of different microhabitats
  • each one may need a different trapping method


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Weather Conditions

  • invertebrate activity strongly influenced by the weather conditions as they are ectothermic
    • generally inactive during cold or wet conditions
    • in any monitoring programme, you need to standardise the weather conditions
      • for example, the Butterfly Conservation guidelines carrying out butterfly transects state that the transect walks should only be carried out in warm (13°C or more), bright weather.
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Time of Day

  • some inverts are diurnal (butterflies and bees) and some are nocturnal (moths and ground beetles)
  • the temperature varies through the day, affecting the activity of most inverts
  • butterfly conservation recommends transects take place between 10am and 5pm
    • more standardised date
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Time of Year

  • many inverts occupy different microhabitats at different life stages, in particular, insects
  • many species have an adult stage lasting only a few weeks, sometimes only a few days
    • need to survey the same site on several occasions throughout the year
  • the best time for inverts is high summer
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Temporarily Storing Live Inverts

  • you need to store animals as you are able to identify and record them.
  • Live inverts should be stored in glass or plastic specimen tubes or jam jars.
  • Insects should be kept dry so that they do not stick to the sides of the container.
  • Freshwater invertebrates should be kept in jam jars or lidded containers half-filled with water from where they are found (not tap water).
  • Predatory inverts, such as dragonfly nymphs, should be stored in separate containers.
  • All samples should be stored in a cool, dry place.
    • Prevent overheating and reduce stress.
  • Should be released as soon as they have been identified.
    • should be released in the same place they were collected.
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Killing and Preserving Inverts

  • We don’t need the big cork borders where specimens are preserved and pinned.
  • However, such collections are maintained at museums and are important for identifying difficult specimens.
  • Insect identification to this level is difficult, often needed a microscope, and will require the specimen to be killed and preserved.
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Trapping Methods

  • These methods on rely on invertebrates actively entering the trap, and are generally cheap and easy to set up.
  • The numbers and species of inverts caught depend on how active they are as well as their abundance, and you need to take this into account when analysing results.
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Pitfall Traps Part 1

  • Used for active, surface living invertebrates.
  • E.g., ground beetles, spiders, springtails, woodlice, millipedes, and centipedes.
  • They consist of a straight-sided container such as a jar or beaker sunk level with the surface of the ground.
  • The traps are easier to find if they are laid out in lines, usually at least 2m apart, or marked with canes.
  • Two different types of pitfall traps:
    • Dry – consist of a container (tin, jar, or drum) buried into the ground with its rim at surface level used to trap mobile animals that fall into it
    • Wet – the same as a dry trap but they contain a solution designed to kill and preserve trapped animals. The fluids that can be used in these traps include formalin (10% formaldehyde), methylated spirits, alcohol, trisodium phosphate, picric acid, or even (With daily checked traps) plain water. A little detergent is usually added to break the surface tension of the liquid to promote quick drowning.
  • Normally covered by a sloped stone or lid to reduce the amount of rain that enters the trap as well as preventing the animals overheating or being eaten by predators.
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Pitfall Traps Part 2

  • Advantages
    • Simple, easily transported, erected and serviced.
    • Easily repeatable between studies and over time.
    • Cost-effective in terms of materials, labour and skills required.
    • Pitfall traps can catch a large number and wide diversity or primarily ground-active inverts
    • Specimens usually caught undamaged and therefore easy to identify
    • Produce a large amount of data
    • Can be set for long periods if necessary
    • Do not require power
  • Disadvantages
    • Not suitable for catching most flying or arboreal inverts, and of limited use with rare ground-dwelling species unless live-capture traps are used.
    • Not suitable for long-term studies as traps can reduce overall abundance of inverts in the local area
    • Can occasionally catch lizards and frogs
    • Not suitable for use in areas where weka are present or in flood-prone areas
    • Except for relative abundance, the method is not suitable for estimating other population parameters
    • Catch is affected by time of year, meteorological conditions and the particular microhabitat
    • Numbers caught can be influenced by attributes of catchable inverts
    • Relative abundance caught in pitfalls differ from their actual relative abundance
    • Studies involving balls are most suitable for qualitative studies such as habitat studies
    • Materials use to make covers may introduce a source of bias
    • Significant problem between increasing structural complexity of vegetation or habitat and capture rate
    • Data collected is typically fraught with problems when it comes to statistical analysis
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Light Traps

  • Used for night-flying insects such as moths.
  • Ultraviolet light such as mercury vapour bulbs attracts the insects.
  • Perspex vanes around the bulb guide them down a funnel into a large container where old egg boxes provide good roosting places.
  • Light traps should be situated away from surrounding foliage.
  • Mostly effective on warm, overcast nights with little wind.
  • Advantages:
    • Easily repeatable
    • Cost-effective in terms of labour and skills required
    • Many types of insect specimens are undamaged and so are good for ID
    • Specimens are easily contained for collection and ID
    • Portable
    • Reward for effort is good.
    • Components of light traps are easily obtained.
  • Disadvantages:
    • Less productive when the weather is cold, wet and windy
    • Less effective near bright artificial lights or when there is bright moonlight.
    • Sometimes less effective when traps set close to fresh water.
    • Minor safety issues associated.
    • Requires a source of electric power, which may be heavy to transport
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Water Traps

  • Used for flying insects such as flies and Hymenopterans (bees, wasps and ants)
  • Half-Fill a washing bowl or ice cream carton with some water with some detergent to break the surface tension.
  • Yellow or white traps are the most effective as they are seen the most by invertebrates.
  • Can be placed high on a stool or on the ground depending on the invertebrates that need to be caught.
  • Advantages
    • Can work to remove pest/invasive species if they are more common than natives
  • Disadvantages
    • Can kill rare species
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Baited Traps

  • Depends on luring invertebrates to the trap with suitable bait.
  • Flies are attracted by decaying meat, and fruit flies are attracted to rotting fruit.  The flies are attracted to a saucer-like container with the bait, then naturally fly upwards through a funnel into a collecting bottle.
  • Moths are attracted to a sugary solution that can be painted on foliage or tree trunks.
  • Slow-moving ground-dwellers such as slugs and snails are attracted to jam or potato placed under a large flat stone or piece of wood on damp ground, rather as gardeners use beer traps. This is also called a cover trap.
  • Advantages
    • More likely to get more data
  • Disadvantages:
    • May encourage unwanted species
    • Individuals may be from further away than your study area due to offering of food
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Flight Interception Traps

  • Consists of a screen of fine black netting and is used to trap flying insects which then drop int collecting trays beneath the netting or, in Malaise traps (complicated and expensive) are guided upwards into a collecting bottle.
  • The collecting trays with hold water with some detergent.
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Collecting Methods

  • Methods depend on the surveyor actively collecting the inverts
    • Direct search with pooters
    • Suction sampler
    • Sweep net
    • Beating tray
    • Transect walk
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  • Useful for collecting smaller, fast-moving species
  • Specimen tube with two pieces of tubing inserted through the bung
  • By sucking the end of one piece of tubing you create reduced pressure in the specimen tube and the invert is drawn up the other piece of tubing.
  • Many inverts easily found by simply looking for them in suitable habitats
    • Always put back stones and logs how you found them
  • Seashore inverts are especially easy to find in the intertidal zone at low tide
  • Tends to be biased towards larger, more active and obvious species but the method can be standardised to collect quantitative data by using timed searcher or by using quadrats.
  • Useful for sampling stream invertebrates
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Sweep Nets

  • Used for invertebrates in long grass such as flies, true bugs, and grasshoppers.
  • They usually have a D-shaped reinforced rim with a deep fine-gauged net, they may be long or short-handled.
  • Sweep the net back and forth through the vegetation finishing by flicking the net up over the frame, trapping the animals inside.
  • Use a pooter to transfer them to specimen tubes.
  • Sweep netting does not work well if the vegetation is wet or less than 15cm high.
  • Butterfly nets are similar to sweep nets.
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Suction Sampler

  • Can be used on vegetation less than 15cm
  • Sucked up into a net.
  • Animals do not usually survive.
  • Two techniques are used.
    • Collecting nozzle is held firmly against the vegetation for a standard length of time, and this is repeated.
    • Known area of vegetation is defined and suction applied.
  • After sampling, net bag is sealed and contents placed in a killing bottle.
  • Inverts then sorted from plant debris and identified.
  • Disadvantages: heavy, prone to breaking, and require regular refuelling
  • Collecting efficiency is usually no greater than sweep netting though sampling tends to be more consistent so they are often preferred in monitoring programmes.
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Beating Trays

  • Used for inverts on bark and tree foliage including beetles, bugs, flies and caterpillars.
  • Tree branches tapped sharply with a stick dislodging the invertebrates which fall onto the beating tray held beneath.
  • Can be a simple piece of white sheeting though commercial ones often have wooden or plastic frames.
  • Pooters can be used to collect inverts from tray. This is a quick and easy way to collect large numbers of inverts.
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Transect Walks

  • Used in the UK national butterfly monitoring scheme under which a weekly recording is carried out from April to September.
  • A set route of 1 to 2km is followed, along which the surveyor walks a slow, steady pace, counting all the butterflies seen within 2.5m either side, and 5m ahead.
  • Butterfly nets can be used to help with ID.
  • Transect walks are only carried out if the temperature is above 13 degrees Celsius with 60% sunshine, or 17 degrees with at least 40%. This method is also used for dragonflies and damselflies.
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Extraction Techniques: Sieving

  • Can be used to separate inverts from various substances, including lead litter, mud, and sand.
  • Start with a broad-gauge mesh, such as a 3mm or 4mm and work down to a 0.5mm mesh, sieving material on to a white cloth or newspaper.
  • Very fine or wet substrates are more easily sorted by ‘wet sieving’ under a flow of water.
  • Inverts can also be separated from soil samples by stirring the sample up in a bucket of water and collecting specimens as they float to the surface.
  • To help them float you can increase the specific gravity by adding sugar or salt but wash the specimens in clean water as soon as possible.
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Extraction Techniques: Tullgren Funnel

  • Tullgren funnels are used to extract invertebrates from loose soil or leaf litter samples
  • These animals like damp, cool environments and move away from hot, dry conditions
  • The apparatus, which can be home-made or commercially bought, consists of a low-wattage light bulb held over a large funnel containing the sample.
  • The animals are driven downwards through gauze in the bottom of the funnel into a beaker of preservative.
  • The funnels are left for several days, then invertebrates are identified and counted.
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Extraction Techniques: Baerman Funnel

  • Used for collecting nematodes, potworms, and rotifers from the film of water around soil particles.
  • Works on a similar principle to Tullgren funnels except that this is a wet extraction method.
  • Here the soil sample is suspended in a bug of muslin in a funnel filled with water.
  • A 60W light bulb heats the funnel, setting up a temperature gradient which drives the animals downwards through the muslin and into the stem of the funnel.
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Extraction Techniques: Chemical Extraction

  • Used to collect earthworms and crane flies.
  • Irritant solution of formaldehyde or potassium permanganate is evenly applied with a watering can to the sample area.
  • The solution penetrates the burrows of the earthworms, driving them to the surface.
  • Collect all invertebrates which emerge in a standard period of time (e.g., 10 minutes) and wash them in clean water.
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