Land insects
8
Once only known from three specimens found in 1963, the robust grasshopper, Brachaspis robustus,
was rediscovered in 1986 in the Ohau and Tekapo riverbeds. It is considered an endangered species.
This chunky, grey, rough-skinned grasshopper is found only along a few sites on riverbeds, terraces
and outwash materials of the Mackenzie Basin.
To avoid predators it relies on its cryptic coloration and remains quite still, rather than actively escaping
by hopping away.
Robust grasshopper
Activities
1
Find out what other grasshoppers live in New Zealand.
2
Other insects found in the Upper Waitaki Basin include boulder butterfly, minute grasshopper, cicadas,
tiger beetle, Tekapo grand weta, grass moth, and chaffer beetle. Working in groups, find out the different
characteristics of moths, butterflies, grasshoppers, cicadas, beetles, and wetas.
3
Look for and describe, the land insects found in your river area. Draw a section of your river and surrounding
vegetation, and where you found the insects.
4
Many people do not know very much about insects. Working in groups, discuss ways in which you could inform
people about insects in a fun way, e.g. by making an 'insect' newspaper, putting on an insect play, making large
drawings of insects for your classroom walls.
5
Insects and other invertebrates are easily overlooked, but they can have profound effects on our lives.
List, and describe, five beneficial and five detrimental invertebrates.
6
Many animals feed on insects. Discuss ways in which insects can avoid being found by predators.
7
Insects are invertebrates. What other sorts of invertebrates are found near rivers and wetlands?
Visit your local river and look for spiders, snails, and so on.
8a
Insect data analysis
The following tables are taken from:
Fraser, Ian. Robust grasshopper (Brachaspis robustus) sightings database and monitoring methods trial.
Project River Recovery Report 99/01, Department of Conservation, Twizel, February 1999
Counts of robust grasshopper (B. robustus) at the Ohau Spit, 10 m transects,
December 1998 and January 1999.
Date
No. B. robustus
Search time
13
4
3
3hr 10m
3hr 30m
3hr 35m
5 December
20 December
4 January
Encounter rate
a)
What was the mean number of robust grasshoppers recorded at the Ohau Spit site?
b)
The encounter rate is the number of grasshoppers seen per hour search.
Fill in the encounter rate column.
Counts of grasshoppers (B. robustus, Sigaus minutus, S. australis) at the Pukaki River,
500 m transects, 5/6 November and 24 November / 3 December 1998.
Date
Species
Number
recorded
No. on riverbed
No. on old river
terrace or
vegetated islands
5-6 November
B. robustus
S. australis
S. minutus
0
33
78
0
20
0
0
13
78
24 Nov & 3 Dec
B. robustus
S. australis
S. minutus
0
18
40
0
9
0
0
9
40
c)
What percentage of S. australis and S. minutus respectively were seen on the riverbed and on
the old river terrace or vegetated islands on 5-6 November and 24 November / 3 December 1998?
d)
What do these percentages tell you about the habitat preferences of S. australis and S. minutus?
e)
What was the total number of grasshoppers seen overall?
f)
What percentages of this number were B. robustus, S. australis and S. minutus?
g)
What does this tell you about the relative abundance of each type of grasshopper at the
Pukaki River in this period?
h)
Measuring insect abundance is difficult. What factors would influence numbers of
grasshoppers seen? How reliable are the above data?