Dung beetles, what is their value?

I get pretty excited when I see dung beetles. They’re an insect we know so much about and that play such an important role in the environment that finding them offers so many opportunities to tell stories. I don’t think we realize how important dung beetles are just because the service they provide is too big to imagine and because they’re cleaning up a mess, we don’t see what it would look like with the mess. A calculation of the value that dung beetles had just for the US cattle industry put it at $380 million. How big do you think the economic value of dung beetles burying wildebeest dung is in the Serengeti? Think about how much dung is produced by 1.5 million wildebeest?

A roller.

The obviously fun to watch dung beetles are the rollers. Rollers come in a lot of different sizes. The male arrives at the dung pile and if the consistency is right, he’ll start to create a ball. Using his perfectly shaped front legs he’ll pat dung into a ball. If you look at his front legs, you’ll notice he’s missing the last joint- basically he doesn’t have the equivalent of insect “hands”. This makes it easier for him to push the ball around. Once he’s happy with his dung ball, he starts to roll it. Navigating using the position of the relative sun (or if it is a nocturnal species the orientation of the milky way or polarized light from the moon), he’ll push it to a place suitable to bury it. In some species, the female will fly in and accompany him, riding on top of the ball. If it is a Scarabeus species, the first ball is a nuptial gift and once they have finished eating they go in search of more to make the brood ball. In one species of roller, Khepher nigroaenus, the female stays with her brood ball and looks after it. In at least one species of dung beetle, excretions from the mouth act to kill any fungus pores in the dung.

The African savannahs have more than 1,500 species of dung beetles. This means there’s intense competition for animal dung which means that you can have as many strategies as species. Most dung beetles fly upwind attracted to the smell of dung. They can tell the difference between different animal dung. Some are specialists and prefer 1 type of animal dung, others are generalist. Over 150 different species of dung beetle have been found attracted to elephant dung, and one famous study in Tsavo National Park (Kenya), researchers counted an incredible 16,000 dung beetles arriving at an elephant dung pile taking it away in less than 2hrs.

There are two other big “groups” of dung beetles, the dwellers who tend to be very small and quick to reproduce, and the tunnelers. Tunnelers aren’t wasting time with rolling, and instead are trying to bury the dung as quickly as possible. In tunnelers the females usually do the tunneling and the males bring down the dung. A pair on the Serengeti can easily bury 250-500gm of dung in night.

Scroll down for a great diagram showing one of the African species and the different stages of the life cycle of the brood ball.

As fascinating as their lifestyle is, the ecological role that they play in the environment. We’ll go into specifics in a different article.

Inanifurahisha sana nikiwaona mende miwa ‘dung beetle’. Dung beetle ni mdudu anayefahamika sana na mwenye umuhimu kwenye mazingira. Endapo tukimpata safarini  sisi tunaopeleka wageni porini, inatupa nafasi ya kueleza hadithi nyingi. Sidhani kama tunauelewa umuhimu wao kikamilifu kwa sababu huduma yao ni kubwa mno. Ukitambua kwamba wanakusanya samadi ya wanyamapori, fikirie pangeonekanaje kama wasingekuwepo. Pangebaki huo uchafu. Hesabu thamani ya kazi yao kwenye tasnia ya ufugaji marekani ni dola milioni 380. Unahisi thamani ya dung beetle kufukia kinyesi cha nyumbu Serengeti ni kiasi gani? Nyumbu milioni moja na nusu hutengeneza kinyesi kiasi gani?

Dung beetle wanaofurahisha zaidi ni wale wanaobiringisha kinyesi. Tunawaita wafiringishaji ‘rollers’. ‘Rollers’ wanapatikana wenye ukubwa tofauti. Dume hua anatangulia kwenye kinyesi na akikuta kinyesi inamfaa huanza kutengeneza mpira. Anatumia miguu yake ya mbele yalioumbwa vizuri kwa ajili ya hiyo kazi kufiringisha kinyesi kama mpira. Ukitazama miguu yake ya mbele utaona kuwa hana vipande vya mwisho- yani hana mikono kama wadudu wengine. Hii inamsaidia kupata nguvu kusukuma huo mpira wa kinyesi. Akifurahia mpira wake anaanza kuusukuma. Anatafuta mwelekeo wa jua kupambazuka na kuzama, hivyo mwelekeo wake ni pembe ya mwanga kutoka kwenye jua, na kama ni aina anayefanya kazi usiku anatumia mwelekeo wa nyota ‘Milky Way’ au mwanga wa nyota za kaskazini ‘polar rays’.  Anausukuma mpira huo wa kinyesi hadi apate sehemu nyeti ya kuifukia chini. Majike ya spishi zingine wanakuja na kumsindikiza wakidandia huo mpira. Kama ni spishi ya familia ya ‘Scarabeus’, huo mpira wa kwanza ni zawadi ya kumchumbia na wakimaliza kula wanaenda kutafuta kinyesi kwa ajili ya kutengeneza mpira wa kutagia (brood ball). Kwa spishi mmoja inayoitwa ‘Khepher nigroaenus’,  jike anabaki na hiyo mpira yenye mayai yake ‘brood ball’ na kuulinda. Kuna spishi zaidi ya mmoja wanaotoa kemikali mdomoni ya kuua kuvu (fungus).

Kuna zaidi ya spishi 1,500 za dung beetle kwenye mbuga ‘savannah’ za Afrika. Inamanisha kuwa kuna upinzani mkubwa kwa ajilia ya kupata kinyesi cha wanyama na husababisha spishi kuwa na mbinu tofauti. Karibia dung beetle zote huruka hewani na kufuata mwelekeo wa upepo ulipotoka wakisikia harufu ya kinyesi. Wanao uwezo wa kutofautisha kinyesi cha wanyama tofauti. Wengine ni wenye maarifa maalum ‘specialist’ na kupenda aina mmoja tu ya kinyesi, lakiini wengine ni kawaida ‘generalist’ ambao hawajali. Zaidi ya spishi 150 za dung beetle wamegunduliwa kupenda kinyesi cha tembo, na utafiti ulifanyika katika hifadhi ya Tsavo (Kenya); walikuta maajabu ya dung beetle 16,000 kufika kwenye kinyesi kimmoja cha tembo na kukimaliza kwa muda chini ya masaa mawili.

Kuna vikundi viwili vingine vya dung beetle. Kuna aina wanaoishi kwenye kinyesi (dwellers) na huwa wanazailiana haraka, na kuna aina wanaofukia chini kinyesi (tunnelers).  Tunnelers hawapotezi muda kwa kufiringisha kinyesi na wanaifukia chini haraka iwezekanavyo. Huwa tunnelers majike yao ndiyo wanachimba handaki na madume hukusanya na kuweka kinyesi ndani ya handaki. Dume na jike Serengeti huweza kufukia gram 250-500 ya kinyesi kwa siku moja.  Hapa kuna mchoro mzuri wa maisha ya dung beetle na hatua za kukua kuanzia yai hadi mdudu mzima.

Maisha yao huvutia lakini umuhimu wao kwenye mazingira ni makubwa. Nitafafanua zaidi kwenye nakali nyingine.

page291image31004768
Image source: The Insects. An Outline of Entomology. 5th Edition. P. J Gullan, P. S Cranston.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s