Sociobiology of the hypogaeic army ant Dorylus (Dichthadia) laevigatus Fr. Smith Dissertation zur Erlangung des naturwissenschaftlichen Doktorgrades der Bayerischen Julius-Maximilians-Universität Würzburg vorgelegt von Stefanie M. Berghoff Geb. in Heessen Würzburg 2002 Eingereicht am: 17. Dezember 2002 Mitglieder der Promotionskommission: Vorsitzender: Dekan Prof. Dr. Rainer Hedrich Gutachter: Prof. Dr. K. Eduard Linsenmair Gutachter: Prof. Dr. Ulrich Maschwitz Tag des Promotionskolloquiums: .................................................................................... Doktorurkunde ausgehändigt am: ..................................................................................... For my parents The awe of army ants “Even man, styled “Lord of creation,” bows to this more numerous foe; for let the Drivers enter one door and he quickly escapes at the other.” (Savage, 1849) “I lost all sense of proportion, forgot my awkward human size, and with a new perspective became an equal of the ants, looking on, watching every passer-by with interest, straining with the bearers of the heavy loads, and breathing more easily when the last obstacle was overcome and home attained.” (Beebe, 1919) Contents Index SUMMARY.................................................................................................................................................................... 1 ZUSAMMENFASSUNG................................................................................................................................................. 3 1. INTRODUCTION........................................................................................................................................................... 5 2. ARMY ANTS – A LIFE HISTORY STRATEGY............................................................................................................ 8 SUMMARY.................................................................................................................................................................... 8 ARMY ANT TRAITS ...................................................................................................................................................... 8 Foraging habits.................................................................................................................................................... 8 Prey ....................................................................................................................................................................... 9 Migrating behavior............................................................................................................................................. 9 Nesting habits ..................................................................................................................................................... 10 Castes within the colony ................................................................................................................................... 10 Workers ........................................................................................................................................................ 10 Queens.......................................................................................................................................................... 10 Males ............................................................................................................................................................ 11 Brood............................................................................................................................................................ 11 Colony reproduction .......................................................................................................................................... 11 Hypogaeic vs. epigaeic species........................................................................................................................ 12 Army ants – a vague definition ........................................................................................................................ 12 3. SETTING THE SCENE: S TUDY SITES , STUDIED SPECIES , AND METHODS EMPLOYED.................................... 14 SUMMARY.................................................................................................................................................................... 14 INTRODUCTION............................................................................................................................................................ 14 STUDY SITES................................................................................................................................................................. 14 STUDIED SPECIES......................................................................................................................................................... 16 STUDY METHODS......................................................................................................................................................... 16 Field methods ...................................................................................................................................................... 17 Soil baits....................................................................................................................................................... 17 Sieve buckets................................................................................................................................................ 17 Sieve cavities............................................................................................................................................... 18 Bucket baits ................................................................................................................................................. 18 Random and search sampling.................................................................................................................. 18 Night observations...................................................................................................................................... 19 Food-choice experiments.......................................................................................................................... 19 Trail excavations........................................................................................................................................ 19 Large-scale excavations............................................................................................................................ 19 Male collections.......................................................................................................................................... 19 Laboratory methods ........................................................................................................................................... 20 Keeping D. laevigatus................................................................................................................................ 20 Formicary experiments.............................................................................................................................. 20 Morphological measurements.................................................................................................................. 21 Genetic analyses......................................................................................................................................... 21 4. FORAGING OF A HYPOGAEIC ARMY ANT: A LONG NEGLECTED MAJORITY................................................... 22 SUMMARY.................................................................................................................................................................... 22 INTRODUCTION............................................................................................................................................................ 22 MATERIALS AND METHODS........................................................................................................................................ 23 Study sites ........................................................................................................................................................... 23 Ant baiting........................................................................................................................................................... 25 Laboratory observations ................................................................................................................................... 26 RESULTS....................................................................................................................................................................... 26 Bait acceptance ................................................................................................................................................... 26 Types of trails and raiding patterns................................................................................................................. 27 The stable hypogaeic trail system............................................................................................................ 27 Column raids on exploratory and secondary trails.............................................................................. 27 Epigaeic swarm raid.................................................................................................................................