diff --git a/tracker/src/main/groovy/com/muwire/tracker/Host.groovy b/tracker/src/main/groovy/com/muwire/tracker/Host.groovy
new file mode 100644
index 00000000..8b38920c
--- /dev/null
+++ b/tracker/src/main/groovy/com/muwire/tracker/Host.groovy
@@ -0,0 +1,27 @@
+package com.muwire.tracker
+
+import com.muwire.core.Persona
+
+/**
+ * A participant in a swarm.  The same persona can be a member of multiple
+ * swarms, but in that case it would have multiple Host objects
+ */
+class Host {
+    final Persona persona
+    long lastPinged
+    long lastResponded
+    volatile String xHave
+    
+    Host(Persona persona) {
+        this.persona = persona
+    }
+    
+    boolean isExpired(long cutoff) {
+        lastPinged > lastResponded && lastResponded <= cutoff 
+    }
+
+    @Override    
+    public String toString() {
+        "Host:[${persona.getHumanReadableName()} lastPinged:$lastPinged lastResponded:$lastResponded xHave:$xHave]"
+    }
+}
diff --git a/tracker/src/main/groovy/com/muwire/tracker/Pinger.groovy b/tracker/src/main/groovy/com/muwire/tracker/Pinger.groovy
new file mode 100644
index 00000000..44073fe1
--- /dev/null
+++ b/tracker/src/main/groovy/com/muwire/tracker/Pinger.groovy
@@ -0,0 +1,14 @@
+package com.muwire.tracker
+
+import org.springframework.stereotype.Component
+
+import com.muwire.core.Core
+
+@Component
+class Pinger {
+    private final Core core
+    
+    Pinger(Core core) {
+        this.core = core
+    }
+}
diff --git a/tracker/src/main/groovy/com/muwire/tracker/Swarm.groovy b/tracker/src/main/groovy/com/muwire/tracker/Swarm.groovy
new file mode 100644
index 00000000..21a46587
--- /dev/null
+++ b/tracker/src/main/groovy/com/muwire/tracker/Swarm.groovy
@@ -0,0 +1,133 @@
+package com.muwire.tracker
+
+import java.util.function.Function
+
+import com.muwire.core.InfoHash
+import com.muwire.core.Persona
+
+import groovy.util.logging.Log
+
+/**
+ * A swarm for a given file
+ */
+@Log
+class Swarm {
+    private final InfoHash infoHash
+    
+    /** 
+     * Invariant: these four collections are mutually exclusive.
+     * A given host can be only in one of them at the same time.
+     */
+    private final Map<Persona,Host> seeds = new HashMap<>()
+    private final Map<Persona,Host> leeches = new HashMap<>()
+    private final Map<Persona,Host> unknown = new HashMap<>()
+    private final Set<Persona> negative = new HashSet<>()
+    
+    /**
+     * hosts which are currently being pinged.  Hosts can be in here
+     * and in the collections above, except for negative.
+     */
+    private final Map<Persona, Host> inFlight = new HashMap<>()
+    
+    Swarm(InfoHash infoHash) {
+        this.infoHash = infoHash
+    }
+    
+    /**
+     * @param cutoff expire hosts older than this
+     */
+    synchronized void expire(long cutoff) {
+        doExpire(cutoff, seeds)
+        doExpire(cutoff, leeches)
+        doExpire(cutoff, unknown)
+    }
+    
+    private static void doExpire(long cutoff, Map<Persona,Host> map) {
+        for (Iterator<Persona> iter = map.keySet().iterator(); iter.hasNext();) {
+            Persona p = iter.next()
+            Host h = map.get(p)
+            if (h.isExpired(cutoff))
+                iter.remove()
+        }
+    }
+    
+    synchronized boolean needsQuery() {
+        seeds.isEmpty() &&
+            leeches.isEmpty() &&
+            inFlight.isEmpty() &&
+            unknown.isEmpty()
+    }
+    
+    synchronized boolean isHealthy() {
+        !seeds.isEmpty()
+        // TODO add xHave accumulation of leeches 
+    }
+    
+    synchronized void add(Persona p) {
+        if (!(seeds.containsKey(p) || leeches.containsKey(p) || 
+            negative.contains(p) || inFlight.containsKey(p)))
+            unknown.computeIfAbsent(p, {new Host(it)} as Function)
+    }
+    
+    synchronized void handleResponse(Host responder, int code) {
+        Host h = inFlight.remove(responder.persona)
+        if (responder != h)
+            log.warning("received a response mismatch from host $responder vs $h")
+            
+        responder.lastResponded = System.currentTimeMillis()    
+        switch(code) {
+            case 200: addSeed(responder); break
+            case 206 : addLeech(responder); break;
+            default :
+            addNegative(responder)
+        }
+    }
+    
+    synchronized void fail(Host failed) {
+        Host h = inFlight.remove(failed.persona)
+        if (h != failed)
+            log.warning("failed a host that wasn't in flight $failed vs $h")
+    }
+    
+    private void addSeed(Host h) {
+        leeches.remove(h.persona)
+        unknown.remove(h.persona)
+        seeds.put(h.persona, h)
+    }
+    
+    private void addLeech(Host h) {
+        unknown.remove(h.persona)
+        seeds.remove(h.persona)
+        leeches.put(h.persona, h)
+    }
+    
+    private void addNegative(Host h) {
+        unknown.remove(h.persona)
+        seeds.remove(h.persona)
+        leeches.remove(h.persona)
+        negative.add(h.persona)
+    }
+    
+    synchronized List<Host> getBatchToPing(int max) {
+        List<Host> rv = new ArrayList<>()
+        rv.addAll(unknown.values())
+        rv.addAll(seeds.values())
+        rv.addAll(leeches.values())
+        rv.removeAll(inFlight.values())
+        
+        Collections.sort(rv, {l, r ->
+            Long.compare(l.lastPinged, r.lastPinged)
+        } as Comparator<Host>)
+        
+        if (rv.size() > max)
+            rv = rv[0..(max-1)]
+        
+        final long now = System.currentTimeMillis()
+        rv.each {
+            it.lastPinged = now
+            inFlight.put(it.persona, it)
+        }
+        
+        rv
+    }
+}
diff --git a/tracker/src/main/groovy/com/muwire/tracker/SwarmManager.groovy b/tracker/src/main/groovy/com/muwire/tracker/SwarmManager.groovy
new file mode 100644
index 00000000..3f4cf8bc
--- /dev/null
+++ b/tracker/src/main/groovy/com/muwire/tracker/SwarmManager.groovy
@@ -0,0 +1,64 @@
+package com.muwire.tracker
+
+import java.util.concurrent.ConcurrentHashMap
+import java.util.function.Function
+
+import javax.annotation.PostConstruct
+
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.stereotype.Component
+
+import com.muwire.core.Core
+import com.muwire.core.InfoHash
+import com.muwire.core.search.QueryEvent
+import com.muwire.core.search.SearchEvent
+import com.muwire.core.search.UIResultBatchEvent
+import com.muwire.core.util.DataUtil
+
+import groovy.util.logging.Log
+import net.i2p.crypto.DSAEngine
+import net.i2p.data.Signature
+
+@Component
+@Log
+class SwarmManager {
+    @Autowired
+    private Core core
+    
+    @Autowired
+    private Pinger pinger
+    
+    private final Map<InfoHash, Swarm> swarms = new ConcurrentHashMap<>()
+    
+    @PostConstruct
+    public void postConstruct() {
+        core.eventBus.register(UIResultBatchEvent.class, this)
+    }
+    
+    void onUIResultBatchEvent(UIResultBatchEvent e) {
+        InfoHash ih = e.results[0].infohash
+        Swarm swarm = swarms.get(ih)
+        if (swarm == null) {
+            log.warning("no swarm found for result with infoHash $ih")
+            return
+        }
+        
+        swarm.add(e.results[0].sender)            
+    }
+    
+    void track(InfoHash infoHash) {
+        Swarm swarm = swarms.computeIfAbsent(infoHash, {new Swarm(it)} as Function)
+        if (swarm.needsQuery()) {
+            UUID uuid = UUID.randomUUID()
+            def searchEvent = new SearchEvent(searchHash : infoHash.getRoot(), uuid: uuid, oobInfohash: true, compressedResults : true, persona : core.me)
+            byte [] payload = infoHash.getRoot()
+            boolean firstHop = core.muOptions.allowUntrusted || core.muOptions.searchExtraHop
+            
+            Signature sig = DSAEngine.getInstance().sign(payload, core.spk) 
+            long timestamp = System.currentTimeMillis()
+            core.eventBus.publish(new QueryEvent(searchEvent : searchEvent, firstHop : firstHop,
+            replyTo: core.me.destination, receivedOn: core.me.destination,
+            originator : core.me, sig : sig.data, queryTime : timestamp, sig2 : DataUtil.signUUID(uuid, timestamp, core.spk)))
+        }
+    }
+}
diff --git a/tracker/src/main/groovy/com/muwire/tracker/Tracker.groovy b/tracker/src/main/groovy/com/muwire/tracker/Tracker.groovy
index 2fdc50f8..2ec3c2a7 100644
--- a/tracker/src/main/groovy/com/muwire/tracker/Tracker.groovy
+++ b/tracker/src/main/groovy/com/muwire/tracker/Tracker.groovy
@@ -122,6 +122,11 @@ class Tracker {
         
     }
     
+    @Bean
+    Core core() {
+        core
+    }
+    
     @Bean
     WebServerFactoryCustomizer<ConfigurableWebServerFactory> wsCustomizer() {
         wsCustomizer
diff --git a/tracker/src/main/groovy/com/muwire/tracker/TrackerService.java b/tracker/src/main/groovy/com/muwire/tracker/TrackerService.java
index aaae77c2..4ace8c46 100644
--- a/tracker/src/main/groovy/com/muwire/tracker/TrackerService.java
+++ b/tracker/src/main/groovy/com/muwire/tracker/TrackerService.java
@@ -2,4 +2,5 @@ package com.muwire.tracker;
 
 public interface TrackerService {
     public TrackerStatus status();
+    public void track(String infoHash);
 }
diff --git a/tracker/src/main/groovy/com/muwire/tracker/TrackerServiceImpl.groovy b/tracker/src/main/groovy/com/muwire/tracker/TrackerServiceImpl.groovy
index 573ad1c7..2790c146 100644
--- a/tracker/src/main/groovy/com/muwire/tracker/TrackerServiceImpl.groovy
+++ b/tracker/src/main/groovy/com/muwire/tracker/TrackerServiceImpl.groovy
@@ -1,13 +1,23 @@
 package com.muwire.tracker
 
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.stereotype.Component
+
 import com.muwire.core.Core
+import com.muwire.core.InfoHash
 import com.muwire.core.UILoadedEvent
 
+import net.i2p.data.Base64
+
+@Component
 class TrackerServiceImpl implements TrackerService {
     
     private final TrackerStatus status = new TrackerStatus()
     private final Core core
     
+    @Autowired
+    private SwarmManager swarmManager
+    
     TrackerServiceImpl(Core core) {
         this.core = core
         status.status = "Starting"
@@ -22,4 +32,10 @@ class TrackerServiceImpl implements TrackerService {
     void onUILoadedEvent(UILoadedEvent e) {
         status.status = "Running"
     }
+    
+    @Override
+    public void track(String infoHash) {
+        InfoHash ih = new InfoHash(Base64.decode(infoHash))
+        swarmManager.track(ih)
+    }
 }